Showing papers by "University of Wisconsin-Madison published in 1990"
TL;DR: In this paper, the invariance proposition of public goods and the optimal tax treatment of charitable giving are discussed. And the authors show that impure altruism is more consistent with observed patterns of giving than the conventional pure altruism approach, and has policy implications that may differ widely from those of the conventional models.
Abstract: When people make donations to privately provided public goods, such as charity, there may be many factors influencing their decision other than altruism. Social pressure, guilt, sympathy, or simply a desire for a "warm glow" may all be important. This paper considers such impure altruism formally and develops a wide set of implications. In particular, this paper discusses the invariance proposition of public goods, solves for the sufficient conditions for neutrality to hold, examines the optimal tax treatment of charitable giving, and calibrates the model based on econometric studies in order to consider policy experiments. Impure altruism is shown to be more consistent with observed patterns of giving than the conventional pure altruism approach, and to have policy implications that may differ widely from those of the conventional models. Copyright 1990 by Royal Economic Society.
5,139 citations
TL;DR: RNA and DNA expression vectors containing genes for chloramphenicol acetyltransferase, luciferase, and beta-galactosidase were separately injected into mouse skeletal muscle in vivo and expression was comparable to that obtained from fibroblasts transfected in vitro under optimal conditions.
Abstract: RNA and DNA expression vectors containing genes for chloramphenicol acetyltransferase, luciferase, and beta-galactosidase were separately injected into mouse skeletal muscle in vivo. Protein expression was readily detected in all cases, and no special delivery system was required for these effects. The extent of expression from both the RNA and DNA constructs was comparable to that obtained from fibroblasts transfected in vitro under optimal conditions. In situ cytochemical staining for beta-galactosidase activity was localized to muscle cells following injection of the beta-galactosidase DNA vector. After injection of the DNA luciferase expression vector, luciferase activity was present in the muscle for at least 2 months.
4,022 citations
TL;DR: Adjuvant therapy with levamisole and fluorouracil should be standard treatment for Stage C colon carcinoma, and this approach should be readily adaptable to conventional medical practice.
Abstract: Twelve hundred ninety-six patients with resected colon cancer that either was locally invasive (Stage B2) or had regional nodal involvement (Stage C) were randomly assigned to observation or to treatment for one year with levamisole combined with fluorouracil. Patients with Stage C disease could also be randomly assigned to treatment with levamisole alone. The median follow-up time at this writing is 3 years (range, 2 to 5 1/2). Among the patients with Stage C disease, therapy with levamisole plus fluorouracil reduced the risk of cancer recurrence by 41 percent (P<0.0001). The overall death rate was reduced by 33 percent (P ≈ 0.006). Treatment with levamisole alone had no detectable effect. The results in the patients with Stage B2 disease were equivocal and too preliminary to allow firm conclusions. Toxic effects of levamisole alone were infrequent, usually consisting of mild nausea with occasional dermatitis or leukopenia, and those of levamisole plus fluorouracil were essentially the same as t...
2,063 citations
TL;DR: It is concluded that gender differences in mathematics performance are small, and the lower performance of women in problem solving that is evident in high school requires attention.
Abstract: Reviewers have consistently concluded that males perform better on mathematics tests than females do. To make a refined assessment of the magnitude of gender differences in mathematics performance, we performed a meta-analysis of 100 studies. They yielded 254 independent effect sizes, representing the testing of 3,175,188 Ss. Averaged over all effect sizes based on samples of the general population, d was -0.05, indicating that females outperformed males by only a negligible amount. For computation, d was -0.14 (the negative value indicating superior performance by females). For understanding of mathematical concepts, d was -0.03; for complex problem solving, d was 0.08. An examination of age trends indicated that girls showed a slight superiority in computation in elementary school and middle school. There were no gender differences in problem solving in elementary or middle school; differences favoring men emerged in high school (d = 0.29) and in college (d = 0.32). Gender differences were smallest and actually favored females in samples of the general population, grew larger with increasingly selective samples, and were largest for highly selected samples and samples of highly precocious persons. The magnitude of the gender difference has declined over the years; for studies published in 1973 or earlier d was 0.31, whereas it was 0.14 for studies published in 1974 or later. We conclude that gender differences in mathematics performance are small. Nonetheless, the lower performance of women in problem solving that is evident in high school requires attention.
1,709 citations
TL;DR: A general, nonlinear mixed effects model for repeated measures data and define estimators for its parameters are proposed and Newton-Raphson estimation is implemented using previously developed computational methods for nonlinear fixed effects models and for linear mixed effects models.
Abstract: We propose a general, nonlinear mixed effects model for repeated measures data and define estimators for its parameters. The proposed estimators are a natural combination of least squares estimators for nonlinear fixed effects models and maximum likelihood (or restricted maximum likelihood) estimators for linear mixed effects models. We implement Newton-Raphson estimation using previously developed computational methods for nonlinear fixed effects models and for linear mixed effects models. Two examples are presented and the connections between this work and recent work on generalized linear mixed effects models are discussed.
1,684 citations
TL;DR: In this article, a conceptual framework that organizes the purchasing arrangements for repetitively used industrial supplies assume many different forms, and a transaction cost analysis is used to organize these forms.
Abstract: Purchasing arrangements for repetitively used industrial supplies assume many different forms. Drawing on transaction cost analysis, the authors advance a conceptual framework that organizes these ...
1,682 citations
TL;DR: A new kind of graph to represent programs is introduced, called a system dependence graph, which extends previous dependence representations to incorporate collections of procedures (with procedure calls) rather than just monolithic programs.
Abstract: The notion of a program slice, originally introduced by Mark Weiser, is useful in program debugging, automatic parallelization, and program integration. A slice of a program is taken with respect to a program point p and a variable x; the slice consists of all statements of the program that might affect the value of x at point p. This paper concerns the problem of interprocedural slicing—generating a slice of an entire program, where the slice crosses the boundaries of procedure calls. To solve this problem, we introduce a new kind of graph to represent programs, called a system dependence graph, which extends previous dependence representations to incorporate collections of procedures (with procedure calls) rather than just monolithic programs. Our main result is an algorithm for interprocedural slicing that uses the new representation. (It should be noted that our work concerns a somewhat restricted kind of slice: rather than permitting a program to b e sliced with respect to program point p and an arbitrary variable, a slice must be taken with respect to a variable that is defined or used at p.)The chief difficulty in interprocedural slicing is correctly accounting for the calling context of a called procedure. To handle this problem, system dependence graphs include some data dependence edges that represent transitive dependences due to the effects of procedure calls, in addition to the conventional direct-dependence edges. These edges are constructed with the aid of an auxiliary structure that represents calling and parameter-linkage relationships. This structure takes the form of an attribute grammar. The step of computing the required transitive-dependence edges is reduced to the construction of the subordinate characteristic graphs for the grammar's nonterminals.
1,663 citations
TL;DR: These findings illustrate the utility of using facial behavior to verify the presence of emotion, are consistent with the notion of emotion-specific physiological patterning, and underscore the importance of anterior cerebral asymmetries for emotions associated with approach and withdrawal.
Abstract: In this experiment, we combined the measurement of observable facial behavior with simultaneous measures of brain electrical activity to assess patterns of hemispheric activation in different regions during the experience of happiness and disgust. Disgust was found to be associated with right-sided activation in the frontal and anterior temporal regions compared with the happy condition. Happiness was accompanied by left-sided activation in the anterior temporal region compared with disgust. No differences in asymmetry were found between emotions in the central and parietal regions. When data aggregated across positive films were compared to aggregate negative film data, no reliable differences in brain activity were found. These findings illustrate the utility of using facial behavior to verify the presence of emotion, are consistent with the notion of emotion-specific physiological patterning, and underscore the importance of anterior cerebral asymmetries for emotions associated with approach and withdrawal.
1,591 citations
TL;DR: In a pedigree derived from a mouse treated with the mutagen ethylnitrosourea, a mutation has been identified that predisposes to spontaneous intestinal cancer.
Abstract: In a pedigree derived from a mouse treated with the mutagen ethylnitrosourea, a mutation has been identified that predisposes to spontaneous intestinal cancer. The mutant gene was found to be dominantly expressed and fully penetrant. Affected mice developed multiple adenomas throughout the entire intestinal tract at an early age.
1,556 citations
TL;DR: A contingency theory is proposed in which communication strategy moderates the impact of channel conditions (structure, climate, and power) on channel outcomes (coordination, satisfaction, commitment, and performance).
Abstract: Though the marketing literature acknowledges that communication plays a vital role in channel functioning, it provides no integrated theory for channel communication. The authors build a theoretica...
1,504 citations
TL;DR: HLA-G is subject to both cell type-specific and developmental regulation and is expressed in early gestation human cytotrophoblasts and is present in choriocarcinoma cell lines studied.
Abstract: The alpha chain of the human histocompatibility antigen HLA-G was identified as an array of five 37- to 39-kilodalton isoforms by the use of two-dimensional gel electrophoresis. Both cell-associated and secreted HLA-G antigens are prominent in first trimester villous cytotrophoblasts and are greatly reduced in third trimester cytotrophoblasts. Allelic variation was not detected, an indication that HLA-G is not obviously polymorphic in cytotrophoblasts. Among the following choriocarcinoma cell lines studied, HLA-G is expressed in JEG but not in Jar or BeWo. Expression of endogenous HLA-G genes has not been found in normal lymphoid cells. Thus, HLA-G is subject to both cell type-specific and developmental regulation and is expressed in early gestation human cytotrophoblasts.
TL;DR: The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust before there were any measurements of the UV properties of interstellar extinction as mentioned in this paper.
Abstract: The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust Before there were any measurements of the UV properties of interstellar extinction, interstellar particles were believed to be composed primarily of dirty ices The maximum of the interstellar extinction was believed to be at 03 μm, the shortest wavelength then observable Both of these predictions were quite wrong (as are probably many of our present ideas regarding dust) The first rocket measurement (Stecher, 1965) showed that there is a very strong extinction feature at 022 μm Now we also know the extinction increases dramatically towards the shortest wavelengths which can be reliably measured to date
07 Oct 1990
TL;DR: In this article, the performance of a high-power, high-density DC-to-DC converter based on the single-phase dual active bridge (DAB) topology is described.
Abstract: The performance of a high-power, high-power-density DC-to-DC converter based on the single-phase dual active bridge (DAB) topology is described. The dual active bridge converter has been shown to have very attractive features in terms of low device and component stresses, small filter components, low switching losses, high power density and high efficiency, bidirectional power flow, buck-boost operation, and low sensitivity to system parasitics. For high output voltages, on the order of kilovolts, a cascaded output structure is considered. The effects of snubber capacitance and magnetizing inductance on the soft switching region of control are discussed. Various control schemes are outlined. Coaxial transformer design techniques have been utilized to carefully control leakage inductance. The layout and experimental performance of a prototype 50 kW 50 kHz unit operating with an input voltage of 200 V DC and an output voltage of 1600 V DC are presented. >
TL;DR: The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscope and a metastable 3D cluster phase with well-defined structure and shape is found.
Abstract: The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscopy. A metastable 3D cluster phase with well-defined structure and shape is found. The clusters have a {105} facet structure. Results suggest that these clusters define the kinetic path for formation of ``macroscopic'' Ge islands.
TL;DR: Fama and Jensen as discussed by the authors argued that the individual owner has little interest in conducting, or even closely monitoring, the day-to-day activities in all of the firms in which he or she has a financial interest.
Abstract: Managers of contemporary publicly held organisations typically are not the owners. Rather, a specialisation of responsibilities has evolved whereby managers coordinate activities within the firm and position it appropriately in its competitive environment; the owners of the firm bear financial risk in the hope of retaining the difference between the firm’s productive cash-flows and the outflows of its promised payments (Fama and Jensen 1983a, 1983b). As the firm’s owners would suffer tremendous financial losses if the firm failed, they tend to diversify their holdings across a variety of firms as a hedge against such a possibility. As a result, the individual owner has little interest in conducting, or even closely monitoring, the day-to-day activities in all of the firms in which he or she has a financial interest (Fama 1980). The owners hire boards of directors who, in turn, hire managers to perform these duties.
TL;DR: The following section describes the tools built to test the utilities, including the fuzz (random character) generator, ptyjig (to test interactive utilities), and scripts to automate the testing process.
Abstract: The following section describes the tools we built to test the utilities. These tools include the fuzz (random character) generator, ptyjig (to test interactive utilities), and scripts to automate the testing process. Next, we will describe the tests we performed, giving the types of input we presented to the utilities. Results from the tests will follow along with an analysis of the results, including identification and classification of the program bugs that caused the crashes. The final section presents concluding remarks, including suggestions for avoiding the types of problems detected by our study and some commentary on the bugs we found. We include an Appendix with the user manual pages for fuzz and ptyjig.
TL;DR: The diagnosis of breast cytology is used to demonstrate the applicability ofMultisurface pattern separation to medical diagnosis and decision making and it is found that this mathematical method is applicable to other medical diagnostic and decision-making problems.
Abstract: Multisurface pattern separation is a mathematical method for distinguishing between elements of two pattern sets. Each element of the pattern sets is comprised of various scalar observations. In this paper, we use the diagnosis of breast cytology to demonstrate the applicability of this method to medical diagnosis and decision making. Each of 11 cytological characteristics of breast fine-needle aspirates reported to differ between benign and malignant samples was graded 1 to 10 at the time of sample collection. Nine characteristics were found to differ significantly between benign and malignant samples. Mathematically, these values for each sample were represented by a point in a nine-dimensional space of real variables. Benign points were separated from malignant ones by planes determined by linear programming. Correct separation was accomplished in 369 of 370 samples (201 benign and 169 malignant). In the one misclassified malignant case, the fine-needle aspirate cytology was so definitely benign and the cytology of the excised cancer so definitely malignant that we believe the tumor was missed on aspiration. Our mathematical method is applicable to other medical diagnostic and decision-making problems.
TL;DR: The authors argue that financial instability occurs when entrepreneurs who want to undertake investment projects have low net worth; the heavy reliance on external finance that this implies causes the agency costs of investment to be high.
Abstract: Financial stability is an important goal of policy, but the relation of financial stability to economic performance and even the meaning of the term itself are poorly understood. This paper explores these issues in a theoretical model. We argue that financial instability, or fragility, occurs when entrepreneurs who want to undertake investment projects have low net worth; the heavy reliance on external finance that this implies causes the agency costs of investment to be high. High agency costs in turn lead to low and inefficient investment. Standard policies for fighting financial fragility can be interpreted as transfers that maintain or increase the net worth of potential borrowers.
TL;DR: The literature on altruism in social psychology, and to a lesser degree in sociology, economics, political behavior and sociobiology since the early 1980's is reviewed in this article.
Abstract: The literature on altruism in social psychology, and to a lesser degree in sociology, economics, political behavior and sociobiology since the early 1980’s is reviewed. The authors take the position that in all of these areas, there appears to be a “paradigm shift” away from the earlier position that behavior that appears to be altruistic must, under closer scrutiny, be revealed as reflecting egoistic motives. Rather, theory and data now being advanced are more compatible with the view that true altruism—acting with the goal of benefitting another—does exist and is a part of human nature. Research in social psychology during the 80’s had a decreased emphasis on situational determinants of helping. Rather, it has focussed mainly on the following topics: the existence and nature of the altruistic personality, the debate concerning the nature of the motivation underlying helping behavior, and the nature of the process of the development of altruism in children and adults. During this time there has also been...
TL;DR: The T gene is isolated using a combination of molecular and genetic techniques, thus making molecular tools available to study processes underlying mesoderm formation in the mouse.
Abstract: The murine developmental mutation T identifies an essential gene in mesoderm formation. Embryos lacking normal gene activity fail to form the notochord, the entire posterior region and the allantois, and die at about 10 days of gestation. We have isolated the T gene using a combination of molecular and genetic techniques, thus making molecular tools available to study processes underlying mesoderm formation in the mouse.
TL;DR: In this paper, the authors reexamine black-white differences in sociopolitical participation and find that empowerment influences black participation by contributing to a more trusting and efficacious orientation to politics and by greatly increasing black attentiveness to political affairs.
Abstract: Using 1987 national sample survey data that included a large black oversample, we reexamine black-white differences in sociopolitical participation. We hypothesized that increases in black empowerment would affect the level of black sociopolitical participation and change the nature of black-white differences in political behavior. The results show that blacks in high-black-empowerment areas—as indicated by control of the mayor's office—are more active than either blacks living in low-empowerment areas or their white counterparts of comparable socioeconomic status. Furthermore, the results show that empowerment influences black participation by contributing to a more trusting and efficacious orientation to politics and by greatly increasing black attentiveness to political affairs. We discuss the results' implications for theoretical interpretations of when and why black sociopolitical behavior differs from that of whites.
TL;DR: The authors proposed a cognitive-neo-associationistic model to account for the effects of negative affect on the development of angry feelings and the display of emotional aggression, which can integrate the core aspect of the James-Lange theory with newer cognitive theories of emotion.
Abstract: Noting that a wide variety of unpleasant feelings, including sadness and depression, apparently can give rise to anger and aggression, I propose a cognitive-neoassociationistic model to account for the effects of negative affect on the development of angry feelings and the display of emotional aggression. Negative affect tends to activate ideas, memories, and expressive-motor reactions associated with anger and aggression as well as rudimentary angry feelings. Subsequent thought involving attributions, appraisals, and schematic conceptions can then intensify, suppress, enrich, or differentiate the initial reactions. Bodily reactions as well as emotion-relevant thoughts can activate the other components of the particular emotion network to which they are linked. Research findings consistent with the model are summarized. Experimental findings are also reported indicating that attention to one's negative feelings can lead to a regulation of the overt effects of the negative affect, I argue that the model can integrate the core aspect of the James-Lange theory with the newer cognitive theories of emotion. Language: en
TL;DR: A longitudinal analysis of the behavior of a birth cohort of 435 boys found that persistence of criminal offending beyond adolescence is predicted for the ADD + delinquent boys.
Abstract: This article describes a longitudinal analysis of the behavior of a birth cohort of 435 boys. 4 groups were defined at age 13 on the basis of both self-reported delinquent behavior and professional diagnosis of Attention Deficit Disorder: ADD + delinquent, ADD only, delinquent only, and nondisordered. Biennial correlates of delinquency (antisocial behavior problems, verbal intelligence, reading difficulty, and family adversity) were traced across childhood. The ADD + delinquent boys consistently fared the worst on the assessments of family adversity, verbal intelligence, and reading. Their antisocial behavior began before school age, escalated at school entry, and persisted into adolescence. The ADD-only boys had normal family, intelligence, and reading scores, and showed only mild antisocial behavior in middle childhood. The delinquent-only boys showed no early risk from family, low intelligence, or reading deficit, and remained relatively free of conduct problems until they initiated delinquency at age 13. Persistence of criminal offending beyond adolescence is predicted for the ADD + delinquent boys.
TL;DR: Biochemical factors which are inherent to the meat itself have received far less research attention and an understanding of these presents the greatest potential for prolonging color stability in fresh meat.
Abstract: The color of fresh meat is an extremely important characteristic influencing the consumer's purchase decision. The stability of pigments in meat is highly variable and is governed by a variety of factors. The effects of exogenous factors (i.e., storage and display conditions) have been well researched. The control of these variables currently offers the best means for maximizing meat color stability. Biochemical factors which are inherent to the meat itself have received far less research attention and an understanding of these presents the greatest potential for prolonging color stability in fresh meat.
TL;DR: The data suggest that the cells in the MSO behave much like cross-correlators, with computer cross correlations of the monaural spike trains were similar to the ITD curve generated binaurally for both correlated and uncorrelated noise signals to the two ears.
Abstract: 1. We studied the sensitivity of cells in the medial superior olive (MSO) of the anesthetized cat to variations in interaural phase differences (IPDs) of low-frequency tones and in interaural time differences (ITDs) of tones and broad-band noise signals. Our sample consisted of 39 cells histologically localized to the MSO. 2. All but one of the cells had characteristic frequencies less than 3 kHz, and 79% were sensitive to ITDs and IPDs. More than one-half (56%) of the cells responded to monaural stimulation of either ear, and both the binaural and monaural responses were highly phase locked. All of the cells that were sensitive to IPDs and monaurally driven by either ear responded in accord with that predicted by the coincidence model of Jeffress, as judged by comparisons of the phases at which the monaural and binaural responses occurred. The optimal IPDs were tightly clustered between 0.0 and 0.2 cycles. Most cells exhibited facilitation of the response at favorable ITDs and inhibition at unfavorable ITDs compared with the monaural responses. 3. Cells in the MSO exhibited characteristic delay, as judged by a linear relationship between the mean interaural phase and stimulating frequency. Characteristic phases were clustered near 0 indicating the most cells responded maximally when the two input tones were in phase. With the use of the binaural beat stimulus we found no differential selectivity for either the direction or speed of interaural phase changes. 4. The cells were also sensitive to ITDs of broad-band noise signals. The ITD curve in response to broad-band noise was similar to that predicted by the composite curve, which was calculated by linearly summating the tonal responses over the frequencies in the response area of the cell. Most (93%) of the peaks of the composite curves were between 0 and +400 microseconds, corresponding to locations in the contralateral sound field. Moreover, computer cross correlations of the monaural spike trains were similar to the ITD curve generated binaurally for both correlated and uncorrelated noise signals to the two ears. Thus our data suggest that the cells in the MSO behave much like cross-correlators. 5. By combining data from different animals and lcoating each cell on a standard MSO, we found evidence for a spatial map of ITDs across the anterior-posterior (A-P) axis of the MSO.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: By analysis of a temperature-sensitive yeast mutant, a heat-shock protein in the matrix of mitochondria, mitochondrial hsp70 (Ssc1p), is found to be involved both in translocation of nuclear-encoded precursor proteins across the mitochondrial membranes and in (re)folding of imported proteins in the Matrix.
Abstract: By analysis of a temperature-sensitive yeast mutant, a heat-shock protein in the matrix of mitochondria, mitochondrial hsp70 (Ssc1p), is found to be involved both in translocation of nuclear-encoded precursor proteins across the mitochondrial membranes and in (re)folding of imported proteins in the matrix.
Journal Article•
TL;DR: Observations indicate that CLA might serve as an in situ defense mechanism against membrane attack by free radicals and may, at least in part, explain the anticarcinogenic properties of CLA.
Abstract: Grilled ground beef contains factors that inhibit the initiation of mouse epidermal carcinogenesis by 7,12-dimethylbenz(a)anthracene. Previously we isolated an active principal and characterized it as an isomeric mixture of conjugated dienoic derivatives of linoleic acid (CLA). We now show that synthetic CLA inhibits the initiation of mouse forestomach tumorigenesis by benzo(a)pyrene. Four and 2 days prior to p.o. treatment with benzo(a)pyrene, female ICR mice were given (a) CLA in olive oil, (b) linoleic acid in olive oil, or (c) olive oil alone or plus 0.85% saline (control groups). Three days later the cycle was repeated for a total of 4 times. At 30 wk of age, the mice were sacrificed. In three independent experiments, mice treated with CLA developed only about half as many neoplasms/animal as mice in the control groups (P
TL;DR: In this article, the influence of climatic and geometric variables on the hourly diffuse fraction has been studied, based on a data set with 22,000 hourly measurements from five European and North American locations.
TL;DR: Gamma as mentioned in this paper is a relational database machine running on an Intel iPSC/2 hypercube with 32 processors and 32 disk drives, where all relations are horizontally partitioned across multiple disk drives enabling relations to be scanned in parallel.
Abstract: The design of the Gamma database machine and the techniques employed in its implementation are described. Gamma is a relational database machine currently operating on an Intel iPSC/2 hypercube with 32 processors and 32 disk drives. Gamma employs three key technical ideas which enable the architecture to be scaled to hundreds of processors. First, all relations are horizontally partitioned across multiple disk drives, enabling relations to be scanned in parallel. Second, parallel algorithms based on hashing are used to implement the complex relational operators, such as join and aggregate functions. Third, dataflow scheduling techniques are used to coordinate multioperator queries. By using these techniques, it is possible to control the execution of very complex queries with minimal coordination. The design of the Gamma software is described and a thorough performance evaluation of the iPSC/s hypercube version of Gamma is presented. >
TL;DR: This work has identified PSF in the MHC class II region by deletion mapping in mutants and chromosome-walking, suggesting that it operates in the intracellular transport of peptides.
Abstract: MAJOR histocompatibility complex (MHC) class I molecules export peptides to the cell surface for surveillance by cytotoxic T lymphocytes1-3. Intracellular peptide binding is critical for the proper assembly and transport of class I molecules4–6. This mechanism is impaired as a result of a non-functional peptide supply factor gene (PSF) in several human mutant cell lines with genomic lesions in the MHC. We have now identified PSF in the MHC class II region by deletion mapping in mutants and chromosome-walking. PSF is homologous to mammalian and bacterial ATP-dependent transport proteins, suggesting that it operates in the intracellular transport of peptides.