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Showing papers in "Science in 1994"


Journal ArticleDOI
23 Dec 1994-Science
TL;DR: A highly sensitive assay for measuring telomerase activity was developed in this paper, which showed that telomerases appear to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth.
Abstract: Synthesis of DNA at chromosome ends by telomerase may be necessary for indefinite proliferation of human cells. A highly sensitive assay for measuring telomerase activity was developed. In cultured cells representing 18 different human tissues, 98 of 100 immortal and none of 22 mortal populations were positive for telomerase. Similarly, 90 of 101 biopsies representing 12 human tumor types and none of 50 normal somatic tissues were positive. Normal ovaries and testes were positive, but benign tumors such as fibroids were negative. Thus, telomerase appears to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth.

7,033 citations


Journal ArticleDOI
11 Feb 1994-Science
TL;DR: A complementary DNA for the Aequorea victoria green fluorescent protein produces a fluorescent product when expressed in prokaryotic or eukaryotic cells, which can be used to monitor gene expression and protein localization in living organisms.
Abstract: A complementary DNA for the Aequorea victoria green fluorescent protein (GFP) produces a fluorescent product when expressed in prokaryotic (Escherichia coli) or eukaryotic (Caenorhabditis elegans) cells. Because exogenous substrates and cofactors are not required for this fluorescence, GFP expression can be used to monitor gene expression and protein localization in living organisms.

7,016 citations


Journal ArticleDOI
07 Oct 1994-Science
TL;DR: A strong candidate for the 17q-linked BRCA1 gene, which influences susceptibility to breast and ovarian cancer, has been identified by positional cloning methods.
Abstract: A strong candidate for the 17q-linked BRCA1 gene, which influences susceptibility to breast and ovarian cancer, has been identified by positional cloning methods. Probable predisposing mutations have been detected in five of eight kindreds presumed to segregate BRCA1 susceptibility alleles. The mutations include an 11-base pair deletion, a 1-base pair insertion, a stop codon, a missense substitution, and an inferred regulatory mutation. The BRCA1 gene is expressed in numerous tissues, including breast and ovary, and encodes a predicted protein of 1863 amino acids. This protein contains a zinc finger domain in its amino-terminal region, but is otherwise unrelated to previously described proteins. Identification of BRCA1 should facilitate early diagnosis of breast and ovarian cancer susceptibility in some individuals as well as a better understanding of breast cancer biology.

6,118 citations


Journal ArticleDOI
03 Jun 1994-Science
TL;DR: A previously unrecognized direct signal transduction pathway to the nucleus has been uncovered: IFN-receptor interaction at the cell surface leads to the activation of kinases of the Jak family that phosphorylate substrate proteins called STATs (signal transducers and activators of transcription).
Abstract: Through the study of transcriptional activation in response to interferon alpha (IFN-alpha) and interferon gamma (IFN-gamma), a previously unrecognized direct signal transduction pathway to the nucleus has been uncovered: IFN-receptor interaction at the cell surface leads to the activation of kinases of the Jak family that then phosphorylate substrate proteins called STATs (signal transducers and activators of transcription). The phosphorylated STAT proteins move to the nucleus, bind specific DNA elements, and direct transcription. Recognition of the molecules involved in the IFN-alpha and IFN-gamma pathway has led to discoveries that a number of STAT family members exist and that other polypeptide ligands also use the Jak-STAT molecules in signal transduction.

5,746 citations


Journal ArticleDOI
16 Dec 1994-Science
TL;DR: unique sequences present in more than 90 percent of Kaposi's sarcoma tissues obtained from patients with acquired immunodeficiency syndrome (AIDS) appear to define a new human herpesvirus.
Abstract: Representational difference analysis was used to isolate unique sequences present in more than 90 percent of Kaposi's sarcoma (KS) tissues obtained from patients with acquired immunodeficiency syndrome (AIDS). These sequences were not present in tissue DNA from non-AIDS patients, but were present in 15 percent of non-KS tissue DNA samples from AIDS patients. The sequences are homologous to, but distinct from, capsid and tegument protein genes of the Gammaherpesvirinae, herpesvirus saimiri and Epstein-Barr virus. These KS-associated herpesvirus-like (KSHV) sequences appear to define a new human herpesvirus.

5,493 citations


Journal ArticleDOI
01 Nov 1994-Science
TL;DR: This experiment demonstrates the feasibility of carrying out computations at the molecular level by solving an instance of the directed Hamiltonian path problem with standard protocols and enzymes.
Abstract: The tools of molecular biology were used to solve an instance of the directed Hamiltonian path problem. A small graph was encoded in molecules of DNA, and the "operations" of the computation were performed with standard protocols and enzymes. This experiment demonstrates the feasibility of carrying out computations at the molecular level.

4,266 citations


Journal ArticleDOI
15 Apr 1994-Science
TL;DR: A negative isotropic magnetoresistance effect has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx, which could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized.
Abstract: A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

4,079 citations


Journal ArticleDOI
17 Jun 1994-Science
TL;DR: In this article, the authors found that mutations of human Cu,Zn superoxide dismutase (SOD) contribute to the pathogenesis of familial amyotrophic lateral sclerosis (ALS).
Abstract: Mutations of human Cu,Zn superoxide dismutase (SOD) are found in about 20 percent of patients with familial amyotrophic lateral sclerosis (ALS). Expression of high levels of human SOD containing a substitution of glycine to alanine at position 93--a change that has little effect on enzyme activity--caused motor neuron disease in transgenic mice. The mice became paralyzed in one or more limbs as a result of motor neuron loss from the spinal cord and died by 5 to 6 months of age. The results show that dominant, gain-of-function mutations in SOD contribute to the pathogenesis of familial ALS.

3,958 citations


Journal ArticleDOI
23 Dec 1994-Science
TL;DR: A relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed, which entails synthesis of the desired material within the pores of a nanoporous membrane.
Abstract: Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

3,887 citations


Journal ArticleDOI
30 Sep 1994-Science
TL;DR: This article synthesizes the current state of the genetic dissection of complex traits--describing the methods, limitations, and recent applications to biological problems.
Abstract: Medical genetics was revolutionized during the 1980s by the application of genetic mapping to locate the genes responsible for simple Mendelian diseases. Most diseases and traits, however, do not follow simple inheritance patterns. Genetics have thus begun taking up the even greater challenge of the genetic dissection of complex traits. Four major approaches have been developed: linkage analysis, allele-sharing methods, association studies, and polygenic analysis of experimental crosses. This article synthesizes the current state of the genetic dissection of complex traits--describing the methods, limitations, and recent applications to biological problems.

3,216 citations


Journal ArticleDOI
14 Jan 1994-Science
TL;DR: Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon.
Abstract: Forest systems cover more than 4.1 x 109 hectares of the Earth9s land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately 37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes emitted 1.6 ± 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid- and high-latitude forest sequestered 0.7 ± 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 ± 0.4 petagrams of carbon per year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results suggest that forests could be carbon sinks or sources in the future.

Journal ArticleDOI
22 Apr 1994-Science
TL;DR: The adhesion receptor integrin alpha v beta 3 was identified as a marker of angiogenic vascular tissue in this paper, and it showed a fourfold increase in expression during angiogenesis on the chick chorioallantoic membrane.
Abstract: Angiogenesis depends on the adhesive interactions of vascular cells. The adhesion receptor integrin alpha v beta 3 was identified as a marker of angiogenic vascular tissue. Integrin alpha v beta 3 was expressed on blood vessels in human wound granulation tissue but not in normal skin, and it showed a fourfold increase in expression during angiogenesis on the chick chorioallantoic membrane. In the latter assay, a monoclonal antibody to alpha v beta 3 blocked angiogenesis induced by basic fibroblast growth factor, tumor necrosis factor-alpha, and human melanoma fragments but had no effect on preexisting vessels. These findings suggest that alpha v beta 3 may be a useful therapeutic target for diseases characterized by neovascularization.

Journal ArticleDOI
04 Feb 1994-Science
TL;DR: Verification and validation of numerical models of natural systems is impossible because natural systems are never closed and because model results are always nonunique.
Abstract: Verification and validation of numerical models of natural systems is impossible. This is because natural systems are never closed and because model results are always nonunique. Models can be confirmed by the demonstration of agreement between observation and prediction, but confirmation is inherently partial. Complete confirmation is logically precluded by the fallacy of affirming the consequent and by incomplete access to natural phenomena. Models can only be evaluated in relative terms, and their predictive value is always open to question. The primary value of models is heuristic.

Journal ArticleDOI
15 Apr 1994-Science
TL;DR: Findings suggest that MTS1 mutations are involved in tumor formation in a wide range of tissues.
Abstract: A putative tumor suppressor locus on the short arm of human chromosome 9 has been localized to a region of less than 40 kilobases by means of homozygous deletions in melanoma cell lines. This region contained a gene, Multiple Tumor Suppressor 1 (MTS1), that encodes a previously identified inhibitor (p16) of cyclin-dependent kinase 4. MTS1 was homozygously deleted at high frequency in cell lines derived from tumors of lung, breast, brain, bone, skin, bladder, kidney, ovary, and lymphocyte. Melanoma cell lines that carried at least one copy of MTS1 frequently carried nonsense, missense, or frameshift mutations in the gene. These findings suggest that MTS1 mutations are involved in tumor formation in a wide range of tissues.

Journal ArticleDOI
18 Mar 1994-Science
TL;DR: Monodisperse biodegradable nanospheres were developed from amphiphilic copolymers composed of two biocompatible blocks and exhibited dramatically increased blood circulation times and reduced liver accumulation in mice.
Abstract: Injectable nanoparticulate carriers have important potential applications such as site-specific drug delivery or medical imaging. Conventional carriers, however, cannot generally be used because they are eliminated by the reticulo-endothelial system within seconds or minutes after intravenous injection. To address these limitations, monodisperse biodegradable nanospheres were developed from amphiphilic copolymers composed of two biocompatible blocks. The nanospheres exhibited dramatically increased blood circulation times and reduced liver accumulation in mice. Furthermore, they entrapped up to 45 percent by weight of the drug in the dense core in a one-step procedure and could be freeze-dried and easily redispersed without additives in aqueous solutions.

Journal ArticleDOI
09 Sep 1994-Science
TL;DR: A dramatic phase shift has occurred in Jamaica, producing a system dominated by fleshy macroalgae (more than 90 percent cover), and immediate implementation of management procedures is necessary to avoid further catastrophic damage.
Abstract: Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. In Jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. A dramatic phase shift has occurred, producing a system dominated by fleshy macroalgae (more than 90 percent cover). Immediate implementation of management procedures is necessary to avoid further catastrophic damage.

Journal ArticleDOI
05 Aug 1994-Science
TL;DR: Findings link a signaling pathway in mammalian cells with a pathway in yeast that is responsive to physiological stress.
Abstract: Mammalian cells respond to endotoxic lipopolysaccharide (LPS) by activation of protein kinase cascades that lead to new gene expression. A protein kinase, p38, that was tyrosine phosphorylated in response to LPS, was cloned. The p38 enzyme and the product of the Saccharomyces cerevisiae HOG1 gene, which are both members of the mitogen-activated protein (MAP) kinase family, have sequences at and adjacent to critical phosphorylation sites that distinguish these proteins from most other MAP kinase family members. Both HOG1 and p38 are tyrosine phosphorylated after extracellular changes in osmolarity. These findings link a signaling pathway in mammalian cells with a pathway in yeast that is responsive to physiological stress.

Journal ArticleDOI
29 Jul 1994-Science
TL;DR: In this paper, large ensembles of hippocampal "place cells" were recorded from three rats during spatial behavioral tasks and in slow-wave sleep preceding and following these behaviors, showing an increased tendency to fire together during subsequent sleep, in comparison to sleep episodes preceding the behavioral tasks.
Abstract: Simultaneous recordings were made from large ensembles of hippocampal "place cells" in three rats during spatial behavioral tasks and in slow-wave sleep preceding and following these behaviors. Cells that fired together when the animal occupied particular locations in the environment exhibited an increased tendency to fire together during subsequent sleep, in comparison to sleep episodes preceding the behavioral tasks. Cells that were inactive during behavior, or that were active but had non-overlapping spatial firing, did not show this increase. This effect, which declined gradually during each post-behavior sleep session, may result from synaptic modification during waking experience. Information acquired during active behavior is thus re-expressed in hippocampal circuits during sleep, as postulated by some theories of memory consolidation.

PatentDOI
28 Mar 1994-Science
TL;DR: In this article, a computer-assisted method for identifying protein sequences that fold into a known 3D structure was proposed, based on three key features of each residue's environment within the structure: (1) the total area of the residue's side-chain that is buried by other protein atoms, inaccessible to solvent; (2) the fraction of the side-chains area that is covered by polar atoms (O, N) or water; and (3) the local secondary structure.
Abstract: A computer-assisted method for identifying protein sequences that fold into a known three-dimensional structure. The method determines three key features of each residue's environment within the structure: (1) the total area of the residue's side-chain that is buried by other protein atoms, inaccessible to solvent; (2) the fraction of the side-chain area that is covered by polar atoms (O, N) or water, and (3) the local secondary structure. Based on these parameters, each residue position is categorized into an environment class. In this manner, a three-dimensional protein structure is converted into a one-dimensional environment string. A 3D structure profile table is then created containing score values that represent the frequency of finding any of the 20 common amino acids structures at each position of the environment string. These frequencies are determined from a database of known protein structures and aligned sequences.

Journal ArticleDOI
16 Dec 1994-Science
TL;DR: New insights in understanding of the cell cycle reveal how fidelity is normally achieved by the coordinated activity of cyclin-dependent kinases, checkpoint controls, and repair pathways and how this fidelity can be abrogated by specific genetic changes.
Abstract: Multiple genetic changes occur during the evolution of normal cells into cancer cells. This evolution is facilitated in cancer cells by loss of fidelity in the processes that replicate, repair, and segregate the genome. Recent advances in our understanding of the cell cycle reveal how fidelity is normally achieved by the coordinated activity of cyclin-dependent kinases, checkpoint controls, and repair pathways and how this fidelity can be abrogated by specific genetic changes. These insights suggest molecular mechanisms for cellular transformation and may help to identify potential targets for improved cancer therapies.

Journal ArticleDOI
15 Jul 1994-Science
TL;DR: The crystal structure of a complex containing the core domain of human p53 and a DNA binding site provides a framework for understanding how mutations inactivate it, and supports the hypothesis that DNA binding is critical for the biological activity of p53.
Abstract: Mutations in the p53 tumor suppressor are the most frequently observed genetic alterations in human cancer. The majority of the mutations occur in the core domain which contains the sequence-specific DNA binding activity of the p53 protein (residues 102-292), and they result in loss of DNA binding. The crystal structure of a complex containing the core domain of human p53 and a DNA binding site has been determined at 2.2 angstroms resolution and refined to a crystallographic R factor of 20.5 percent. The core domain structure consists of a beta sandwich that serves as a scaffold for two large loops and a loop-sheet-helix motif. The two loops, which are held together in part by a tetrahedrally coordinated zinc atom, and the loop-sheet-helix motif form the DNA binding surface of p53. Residues from the loop-sheet-helix motif interact in the major groove of the DNA, while an arginine from one of the two large loops interacts in the minor groove. The loops and the loop-sheet-helix motif consist of the conserved regions of the core domain and contain the majority of the p53 mutations identified in tumors. The structure supports the hypothesis that DNA binding is critical for the biological activity of p53, and provides a framework for understanding how mutations inactivate it.

Journal ArticleDOI
24 Jun 1994-Science
TL;DR: Comparison of mice lacking either type I or type II IFN receptors showed that, at least in response to some viruses, both IFN systems are essential for antiviral defense and are functionally nonredundant.
Abstract: Mice lacking the known subunit of the type I interferon (IFN) receptor were completely unresponsive to type I IFNs, suggesting that this receptor chain is essential for type I IFN-mediated signal transduction. These mice showed no overt anomalies but were unable to cope with viral infections, despite otherwise normal immune responses. Comparison of mice lacking either type I or type II IFN receptors showed that, at least in response to some viruses, both IFN systems are essential for antiviral defense and are functionally nonredundant.

Journal ArticleDOI
20 May 1994-Science
TL;DR: Grafted and endogenous SVZ cells in the lateral ventricle of adult mice migrate long distances and differentiate into neurons in the olfactory bulb.
Abstract: During the development of the mammalian brain, neuronal precursors migrate to their final destination from their site of birth in the ventricular and subventricular zones (VZ and SVZ, respectively). SVZ cells in the walls of the lateral ventricle continue to proliferate in the brain of adult mice and can generate neurons in vitro, but their fate in vivo is unknown. Here SVZ cells from adult mice that carry a neuronal-specific transgene were grafted into the brain of adult recipients. In addition, the fate of endogenous SVZ cells was examined by microinjection of tritiated thymidine or a vital dye that labeled a discrete population of SVZ cells. Grafted and endogenous SVZ cells in the lateral ventricle of adult mice migrate long distances and differentiate into neurons in the olfactory bulb.

Journal ArticleDOI
04 Mar 1994-Science
TL;DR: In the predicted hybrid protein, the amino terminus of nucleophosmin (NPM) is linked to the catalytic domain of anaplastic lymphoma kinase (ALK), and unscheduled expression of the truncated ALK may contribute to malignant transformation in these lymphomas.
Abstract: The 2;5 chromosomal translocation occurs in most anaplastic large-cell non-Hodgkin's lymphomas arising from activated T lymphocytes. This rearrangement was shown to fuse the NPM nucleolar phosphoprotein gene on chromosome 5q35 to a previously unidentified protein tyrosine kinase gene, ALK, on chromosome 2p23. In the predicted hybrid protein, the amino terminus of nucleophosmin (NPM) is linked to the catalytic domain of anaplastic lymphoma kinase (ALK). Expressed in the small intestine, testis, and brain but not in normal lymphoid cells, ALK shows greatest sequence similarity to the insulin receptor subfamily of kinases. Unscheduled expression of the truncated ALK may contribute to malignant transformation in these lymphomas.


Journal ArticleDOI
26 Aug 1994-Science
TL;DR: Mucosally derived TH2-like clones induced by oral antigen can actively regulate immune responses in vivo and may represent a different subset of T cells.
Abstract: Experimental autoimmune encephalomyelitis (EAE) is a cell-mediated autoimmune disease that serves as an animal model for multiple sclerosis. Oral administration of myelin basic protein (MBP) suppresses EAE by inducing peripheral tolerance. T cell clones were isolated from the mesenteric lymph nodes of SJL mice that had been orally tolerized to MBP. These clones were CD4+ and were structurally identical to T helper cell type 1 (TH1) encephalitogenic CD4+ clones in T cell receptor usage, major histocompatibility complex restriction, and epitope recognition. However, they produced transforming growth factor-beta with various amounts of interleukin-4 and interleukin-10 and suppressed EAE induced with either MBP or proteolipid protein. Thus, mucosally derived TH2-like clones induced by oral antigen can actively regulate immune responses in vivo and may represent a different subset of T cells.

Journal ArticleDOI
01 Apr 1994-Science
TL;DR: A new family member, Stat3, becomes activated through phosphorylation on tyrosine as a DNA binding protein in response to epidermal growth factor and interleukin-6 but not interferon gamma (IFN-gamma).
Abstract: The STAT family of proteins carries out a dual function: signal transduction and activation of transcription. A new family member, Stat3, becomes activated through phosphorylation on tyrosine as a DNA binding protein in response to epidermal growth factor (EGF) and interleukin-6 (IL-6) but not interferon gamma (IFN-gamma). It is likely that this phosphoprotein forms homodimers as well as heterodimers with the first described member of the STAT family, Stat91 (renamed Stat1 alpha), which is activated by the IFNs and EGF. Differential activation of different STAT proteins in response to different ligands should help to explain specificity in nuclear signaling from the cell surface.

Journal ArticleDOI
30 Sep 1994-Science
TL;DR: This analysis localized a second breast cancer susceptibility locus, BRCA2, to a 6-centimorgan interval on chromosome 13q12-13, which preliminary evidence suggests suggests confers a high risk of breast cancer but does not confer a substantially elevated risk of ovarian cancer.
Abstract: A small proportion of breast cancer, in particular those cases arising at a young age, is due to the inheritance of dominant susceptibility genes conferring a high risk of the disease. A genomic linkage search was performed with 15 high-risk breast cancer families that were unlinked to the BRCA1 locus on chromosome 17q21. This analysis localized a second breast cancer susceptibility locus, BRCA2, to a 6-centimorgan interval on chromosome 13q12-13. Preliminary evidence suggests that BRCA2 confers a high risk of breast cancer but, unlike BRCA1, does not confer a substantially elevated risk of ovarian cancer.

Journal ArticleDOI
18 Mar 1994-Science
TL;DR: A search of a large database of expressed sequence tags derived from random complementary DNA clones revealed three additional human mismatch repair genes, all related to the bacterial mutL gene, demonstrating that this gene is responsible for HNPCC.
Abstract: Some cases of hereditary nonpolyposis colorectal cancer (HNPCC) are due to alterations in a mutS-related mismatch repair gene. A search of a large database of expressed sequence tags derived from random complementary DNA clones revealed three additional human mismatch repair genes, all related to the bacterial mutL gene. One of these genes (hMLH1) resides on chromosome 3p21, within 1 centimorgan of markers previously linked to cancer susceptibility in HNPCC kindreds. Mutations of hMLH1 that would disrupt the gene product were identified in such kindreds, demonstrating that this gene is responsible for the disease. These results suggest that defects in any of several mismatch repair genes can cause HNPCC.

Journal ArticleDOI
15 Apr 1994-Science
TL;DR: Under conditions that allowed only a limited number of molecular pairs to interact, the force required to separate tip and bead was found to be quantized in integer multiples of 160 +/- 20 piconewtons for biotin and 85 +/- 15 piconewstons for iminobiotin.
Abstract: The adhesion force between the tip of an atomic force microscope cantilever derivatized with avidin and agarose beads functionalized with biotin, desthiobiotin, or iminobiotin was measured Under conditions that allowed only a limited number of molecular pairs to interact, the force required to separate tip and bead was found to be quantized in integer multiples of 160 +/- 20 piconewtons for biotin and 85 +/- 15 piconewtons for iminobiotin The measured force quanta are interpreted as the unbinding forces of individual molecular pairs