Showing papers by "University of Vermont published in 1993"

Surgical resection and radiolocalization of the sentinel lymph node in breast cancer using a gamma probe

Abstract: We have recently reported on a technique of gamma probe localization of radiolabelled lymph nodes to identify the sentinel node in malignant melanoma. In order to determine whether this technique is applicable to assist in staging breast cancer, a pilot study was begun to address two questions: (i) can the sentinel lymph node draining a breast cancer be identified for selective resection; and (ii) is the sentinel lymph node predictive of the status of the entire axillary lymph nodes? One to four hours prior to axillary lymph node dissection, 22 consecutive patients had approximately 0.4 mCi of technetium sulfur colloid in 0.5 ml saline injected around the perimeter of the breast lesion. A hand-held gamma counter was used at surgery to locate the lymph node(s) receiving drainage from the breast. A sentinel lymph node was identified in 18 of 22 patients. Of these 18 patients, the sentinel lymph node was positive in seven of seven patients, with pathologically verified metastatic breast cancer to at least one lymph node. In three out of seven patients, the sentinel lymph node was the only lymph node with metastatic cancer. In this pilot study of breast cancer patients, we conclude that: (i) radiolocalization and selective resection of sentinel lymph nodes is possible; and (ii) the sentinel lymph node appears to predict correctly the status of the remaining axilla. These data justify a larger clinical trial to verify the value of this technique.

Depression in adolescence.

Abstract: Adolescence is an important developmental period for understanding the nature, course, and treatment of depression. Recent research concerned with depressive mood, syndromes, and disorders during adolescence is reviewed, including investigations of the prevalence, course, risk factors, and prevention and treatment programs for each of these three levels of depressive phenomena in adolescence. A broad biopsychosocial perspective on adolescent depression is recommended, and possible directions for future integrative research are proposed. Based on current research and knowledge, implications for research, program, and national policy are considered.

Canopy structure and vertical patterns of photosynthesis and related leaf traits in a deciduous forest.

Abstract: Canopy structure and light interception were measured in an 18-m tall, closed canopy deciduous forest of sugar maple (Acer saccharum) in southwestern Wisconsin, USA, and related to leaf structural characteristics, N content, and leaf photosynthetic capacity. Light attenuation in the forest occurred primarily in the upper and middle portions of the canopy. Forest stand leaf area index (LAI) and its distribution with respect to canopy height were estimated from canopy transmittance values independently verified with a combined leaf litterfall and point-intersect method. Leaf mass, N and A max per unit area (LMA, N/area and A max/area, respectively) all decreased continuously by over two-fold from the upper to lower canopy, and these traits were strongly correlated with cumulative leaf area above the leaf position in the canopy. In contrast, neither N concentration nor A max per unit mass varied significantly in relation to the vertical canopy gradient. Since leaf N concentration showed no consistent pattern with respect to canopy position, the observed vertical pattern in N/area is a direct consequence of vertical variation of LMA. N/area and LMA were strongly correlated with A max/area among different canopy positions (r2=0.81 and r2=0.66, respectively), indicating that vertical variation in area-based photosynthetic capacity can also be attributed to variation in LMA. A model of whole-canopy photosynthesis was used to show that observed or hypothetical canopy mass distributions toward higher LMA (and hence higher N/area) in the upper portions of the canopy tended to increase integrated daily canopy photosynthesis over other LMA distribution patterns. Empirical relationships between leaf and canopy-level characteristics may help resolve problems associated with scaling gas exchange measurements made at the leaf level to the individual tree crown and forest canopy-level.

Localization of D1 and D2 dopamine receptors in brain with subtype-specific antibodies.

Abstract: Five or more dopamine receptor genes are expressed in brain However, the pharmacological similarities of the encoded D1-D5 receptors have hindered studies of the localization and functions of the subtypes To better understand the roles of the individual receptors, antibodies were raised against recombinant D1 and D2 proteins and were shown to bind to the receptor subtypes specifically in Western blot and immunoprecipitation studies Each antibody reacted selectively with the respective receptor protein expressed both in cells transfected with the cDNAs and in brain By immunocytochemistry, D1 and D2 had similar regional distributions in rat, monkey, and human brain, with the most intense staining in striatum, olfactory bulb, and substantia nigra Within each region, however, the precise distributions of each subtype were distinct and often complementary D1 and D2 were differentially enriched in striatal patch and matrix compartments, in selective layers of the olfactory bulb, and in either substantia nigra pars compacta or reticulata Electron microscopy demonstrated that D1 and D2 also had highly selective subcellular distributions In the rat neostriatum, the majority of D1 and D2 immunoreactivity was localized in postsynaptic sites in subsets of spiny dendrites and spine heads in rat neostriatum Presynaptic D1 and D2 receptors were also observed, indicating both subtypes may regulate neurotransmitter release D1 was also present in axon terminals in the substantia nigra These results provide a morphological substrate for understanding the pre- and postsynaptic functions of the genetically defined D1 and D2 receptors in discrete neuronal circuits in mammalian brain

cGMP-dependent protein kinase activates Ca-activated K channels in cerebral artery smooth muscle cells.

Abstract: Guanosine-3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (cGMP-PK) plays a central role in the mediation of the vasodilator response to nitric oxide (NO) and other nitrovasodilators. It is unclear whether cGMP-PK affects calcium-activated potassium channels (KCa channels) or any other type of ion channel in smooth muscle. We provide here the first direct evidence that cGMP-PK can activate KCa channels in arterial smooth muscle cells. We demonstrate that NO and a membrane-permeable analogue of cGMP can activate KCa channels in on-cell patches approximately twofold. Furthermore, cGMP-PK, in the presence of ATP and cGMP added directly to the intracellular surface of inside-out patches, increases channel activity by approximately eightfold. These results suggest that cGMP-PK-mediated activation of KCa channels may contribute to the actions of NO and other nitrovasodilators.

Development and Validation of the Biphasic Alcohol Effects Scale

Abstract: Alcohol produces stimulant and sedative effects, and both types of effect are thought to influence drinking practices. This article describes the development and preliminary validation of the Biphasic Alcohol Effects Scale (BAES), a self-report, unipolar adjective rating scale designed to measure both stimulant and sedative effects of alcohol. An initial pool of 12 stimulant and 12 sedative items was derived from previous alcohol effect measures, and from descriptors of intoxication generated by subjects during interviews conducted on both the ascending and descending limbs of the blood alcohol curve. This item pool was administered to a sample of sober college students twice, with a 2-week inter-test interval. Items that were difficult to comprehend, or that had high ratings or low test-retest reliability, were eliminated, resulting in a seven-item stimulant subscale and a seven-item sedative subscale. These subscales showed high internal consistency in a sober state, which was not improved by additional item deletion. The data from this study also provided a basis for revising the instructions for the BAES. The new 14-item instrument was then given to 30 male and 12 female nonalcoholics on the ascending and descending limbs of the blood alcohol curve, after the administration of either 0.75 ml/kg alcohol (males) or 0.65 ml/kg alcohol (females). Internal consistency was high for both BAES subscales on both limbs of the blood alcohol curve (Cronbach's alpha = 0.85 to 0.94), and was not improved by additional item deletion. Factor analyses conducted on both limbs of the blood alcohol curve supported the proposed factor structure of the BAES.(ABSTRACT TRUNCATED AT 250 WORDS)

Achieving cocaine abstinence with a behavioral approach.

Abstract: Objective The authors compared the efficacy of a multicomponent behavioral treatment and drug abuse counseling for cocaine-dependent individuals. Method The 38 patients were enrolled in outpatient treatment and were randomly assigned to the two treatments. Counseling in the behavioral treatment was based on the community reinforcement approach, while the drug abuse counseling was based on the disease model of dependence and recovery. Patients in the behavioral, but not the drug counseling, treatment also received incentives contingent on submitting cocaine-free urine specimens. Results Of the 19 patients who received behavioral treatment, 58% completed 24 weeks of treatment, versus 11% of the patients who received counseling. In the behavioral treatment group 68% and 42% of the patients achieved at least 8 and 16 weeks of documented continuous cocaine abstinence, respectively, versus 11% and 5% in the drug abuse counseling group. Conclusions This multicomponent behavioral treatment appears to be an effective intervention for retaining outpatients in treatment and establishing cocaine abstinence.

Alterations in sarcoplasmic reticulum gene expression in human heart failure. A possible mechanism for alterations in systolic and diastolic properties of the failing myocardium.

Abstract: Recent studies have shown that intracellular Ca2+ handling is abnormal in the myocardium of patients with end-stage heart failure. Muscles from the failing hearts showed a prolonged Ca2+ transient and a diminished capacity to restore a low resting Ca2+ level during diastole. Accordingly, we examined whether this defect in Ca2+ transport function is due to alterations in sarcoplasmic reticulum gene expression. We determined the messenger RNA (mRNA) levels of sarcoplasmic reticulum Ca2+ transport proteins in failing human hearts from 17 cardiac transplant recipients with a diagnosis of dilated cardiomyopathy, primary pulmonary hypertension, or ischemic heart disease. The expression levels of each mRNA were compared with each other and then correlated with that of atrial natriuretic factor (ANF) mRNA in the failing ventricle. The mRNA levels for the calcium release channel (ryanodine receptor, RYR2), Ca2+ uptake pump (Ca(2+)-ATPase, SERCA2 isoform), and phospholamban differed significantly between heart samples but showed an inverse relation with that of ventricular ANF mRNA. In contrast, calsequestrin mRNA levels remained unchanged in these failing hearts. In addition, beta-myosin and alpha-cardiac actin mRNA levels also showed an inverse relation with ANF mRNA levels. These changes were observed in both right and left ventricles of hearts with congestive heart failure due to dilated cardiomyopathy, primary pulmonary hypertension, or ischemic heart disease. The results are consistent with the hypothesis that abnormal calcium handling in the sarcoplasmic reticulum of failing hearts is due to the altered expression of the genes encoding sarcoplasmic reticulum proteins.

Carbohydrate metabolism during pregnancy in control subjects and women with gestational diabetes.

Abstract: The purpose of this study was to characterize carbohydrate metabolism associated with the development of gestational diabetes. Six control (Ctl) and ten women with gestational diabetes mellitus (GDM) were evaluated using an intravenous glucose tolerance test and hyperinsulinemic-euglycemic clamp with [6,6-2H2]glucose prior to conception (P) and at 12-14 (E), and 34-36 wk of gestation (L). There was an increase (P = 0.0001) in first-phase insulin response in Ctl (P 174 +/- 133, E 388 +/- 120, and L 587 +/- 303 microU/ml) and GDM (P 197 +/- 94, E 267 +/- 77, and L 376 +/- 162 microU/ml) but a significant (P = 0.02) lag in change in GDM with advancing gestation. Basal endogenous glucose production increased during gestation [Ctl: P 2.74 +/- 0.23, E 2.62 +/- 0.38, and L 3.14 +/- 0.36; GDM: P 2.68 +/- 0.51, E 2.78 +/- 0.45, and L 2.98 +/- 0.48 mg.kg fat-free mass (FFM)-1 x min-1; P = 0.02], but there was resistance to suppression by insulin infusion (P = 0.03) in late gestation (GDM: 0.61 +/- 0.44 vs. Ctl: 0.16 +/- 0.17 mg.kg FFM-1 x min-1). Insulin sensitivity decreased during gestation (Ctl: P 10.78 +/- 2.78, E 8.34 +/- 2.36, and L 4.75 +/- 1.22; GDM: P 7.49 +/- 2.13, E 7.40 +/- 1.45, and L 4.21 +/- 1.01 mg.kg FFM-1 x min-1; P = 0.0001) and was primarily decreased (P = 0.04) in GDM compared with Ctl from P through E. These findings closely resemble those of non-insulin-dependent, predominantly insulin-resistant diabetes, which is often a sequel of GDM.

Family factors related to children's intrinsic/extrinsic motivational orientation and academic performance.

Abstract: This study examined 3 familial factors--parental surveillance of homework, parental reactions to grades, and general family style--in relation to children's motivational orientation and academic performance. Family, parent, and child measures were obtained in the home from 93 fifth graders and their parents. Teachers provided a measure of classroom motivational orientation, and grades and achievement scores were obtained from school records. Higher parental surveillance of homework, parental reactions to grades that included negative control, uninvolvement, or extrinsic reward, and over- and undercontrolling family styles were found to be related to an extrinsic motivational orientation and to lower academic performance. On the other hand, parental encouragement in response to grades children received was associated with an intrinsic motivational orientation, and autonomy-supporting family styles were associated with intrinsic motivation and higher academic performance. In addition, socioeconomic level was a significant predictor of motivational orientation and academic performance.

Gamma-probe guided localization of lymph nodes.

Abstract: The initial draining lymph node (Sentinel node) of a tumour may reflect the status of the tumours spread to the remaining lymphatic bed. The sentinel node, which has been reported to predict metastatic melanoma, has recently been localized by a new invasive technique [1]. The goal of our pre-clinical trial was to test a non-invasive technique to localize the sentinel node. Gamma-probe guided localization was used to identify and then surgically remove the first draining lymph node(s) in 16 inguinal lymphatic basins of eight cats. This method was found to be comparable to an invasive method using a blue dye. Gamma-probe localization has several potential advantages in that it can: (a) precisely locate on the surface of the skin the position of an underlying lymph node, (b) intraoperatively guide the surgeon to the lymph node during dissection, (c) verify that the correct node has been biopsied, (d) determine the possible presence of residual lymph nodes, (e) allow lymph nodes to be harvested through a small incision as opposed to raising a skin flap, and (f) be rapidly and easily performed.

Atherosclerotic Renovascular Disease and Progressive Renal Failure

Abstract: Purpose: To evaluate information on the prevalence and rate of progression of atherosclerotic renovascular disease and the effect of angiotensin-converting enzyme inhibition on this process, with t...

Gamma-probe-guided lymph node localization in malignant melanoma

Abstract: The initial draining lymph node (sentinel node) has been successfully localized using intraoperative vital dye mapping and reportedly is predictive of regional nodal metastases in Clinical- Stage 1 melanoma [1]. In an animal model, we previously established the technique of gamma-probe-guided localization of the technetium-99 sulfur colloid labelled sentinel node [2] and found its sensitivity equal to vital dye mapping. We now report our initial experience using gamma-probe-guided localization to identify and then surgically remove the first draining lymph node(s) in 10 malignant melanoma patients. Lymphoscintigraphy was used to confirm localization. We conclude that this technique: (a) reliably localizes the sentinel node draining the site of a primary melanoma, (b) allows the lymphatic bed to be checked intraoperatively verifying complete sentinel node biopsy, and (c) is relatively simple and can be performed under local anaesthesia.

“I've Counted Jon”: Transformational Experiences of Teachers Educating Students with Disabilities

Abstract: The purpose of this study was to describe the experiences of general education teachers who have had a student with severe disabilities in their class. Interviews of 19 general education teachers, kindergarten through Grade 9, as well as questionnaires completed by 18 teachers, were analyzed using categorical coding procedures to identify themes related to the teachers' experiences. Results showed that despite teachers' initial negative reactions to the placement of a child with severe disabilities in their classrooms, 17 teachers described transforming experiences of a more positive nature and related many benefits to the students with disabilities, their classmates, and the teachers themselves. Respondents also characterized what support services they found helpful and not helpful.

The Epidemiology of Traumatic Death: A Population-Based Analysis

Abstract: • Despite the proliferation of trauma systems, there are no population-based data describing the epidemiology of traumatic death. To provide these data, we reviewed all trauma deaths occurring in San Diego (California) County during 1 year. There were 625 traumatic deaths during the study (27.3 deaths per 100 000 population per year). Motor vehicle trauma was the most common cause of injury leading to death (N=344 [55.2%]; 15.0 annual deaths per 100 000 population). Central nervous system injuries were the most common cause of death (48.5%, or 13.2 deaths per 100 000 population per year). Sepsis was responsible for only 2.5% of the overall mortality. Based on life-table data, traumatic death resulted in an annual loss of 1091 years of life per 100 000 and an annual loss of 492 years of productivity per 100 000. Injury continues to account for an enormous loss of life despite improvements in survival wrought by trauma systems. (Arch Surg.1993;128:571-575)

Inward rectifier K+ currents in smooth muscle cells from rat resistance-sized cerebral arteries.

Abstract: Inward rectifier K+ channels have been implicated in the control of membrane potential and external K(+)-induced dilations of small cerebral arteries. In the present study, whole cell K+ currents through the inward rectifier K+ channel were measured in single smooth muscle cells isolated from the posterior cerebral artery of Wistar-Kyoto rats. The whole cell K+ current-voltage relationship showed inward rectification. Inward currents were recorded negative to the K+ equilibrium potential, whereas outward currents were small. When extracellular K+ was elevated, the zero current potential shifted to the new K+ equilibrium potential, and the conductance of the inward current increased. Inward currents were reduced by external barium or cesium. Inhibition by barium and cesium increased with membrane hyperpolarization. The half-inhibition constant for barium was 2.2 microM at -60 mV, increasing e-fold for a 23-mV depolarization. We provide the first direct measurements of inward rectifier K+ currents in single smooth muscle cells and show that external barium ions are effective blockers of these currents.

Taxonomy, assessment, and diagnosis of depression during adolescence.

Abstract: Research on depressive phenomena during adolescence has focused on 3 separate constructs: depressed mood, depressive syndromes, and depressive disorders. Approaches to the assessment, taxonomy, and diagnosis of these 3 conceptualizations are reviewed. Each of the approaches is represented by different assessment tools measuring related but distinct aspects of depressive phenomena. The constructs share a common set of symptoms reflecting negative affectivity but differ in their inclusion of symptoms of anxiety, somatic problems, and disrupted concentration and in the duration and severity of the symptoms they include. Depressed mood, syndromes, and disorders are integrated as 3 levels of depressive phenomena in a hierarchical and sequential model, and moderating factors are hypothesized to account for the relationships among the 3 levels. The need for a stronger developmental focus to understand depressive phenomena during adolescence is emphasized.

Subcellular localization of Cdc42p, a Saccharomyces cerevisiae GTP-binding protein involved in the control of cell polarity.

Abstract: The Saccharomyces cerevisiae Cdc42 protein, a member of the Ras superfamily of low-molecular-weight GTP-binding proteins, is involved in the control of cell polarity during the yeast cell cycle. This protein has a consensus sequence (CAAX) for geranylgeranyl modification and is likely to be associated, at least in part, with cell membranes. Using cell fractionation and immunolocalization techniques, we have investigated the subcellular localization of Cdc42p. Cdc42p was found in both soluble and particulate pools, and neither its abundance nor its distribution varied through the cell cycle. The particulate form of Cdc42p could be solubilized with detergents but not with NaCl or urea, suggesting that it is tightly associated with membranes. An increase in soluble Cdc42p was observed in a geranylgeranyltransferase mutant strain (cdc43-2ts) grown at the restrictive temperature. In addition, Cdc42p from a cdc42C188S mutant strain (that has an alteration at the prenylation consensus site) was almost exclusively in the soluble fraction, suggesting that membrane localization is dependent on geranylgeranyl modification at Cys-188. Immunofluorescence and immunoelectron microscopy experiments demonstrated that Cdc42p localizes to the plasma membrane in the vicinity of secretory vesicles that were found at the site of bud emergence, at the tips and sides of enlarging buds, and within mating projections (shmoo tips) in alpha-factor-arrested cells. These results indicate that Cdc42p is localized to the bud site early in the cell cycle and suggest that this localization is critical for the selection of the proper site for bud emergence and for polarized cell growth.

Control of Chemotherapy-Induced Emesis

Abstract: The development of antiemetic drugs has been one of the most rewarding areas of oncologic research, since therapeutic advances in this area can result in immediate improvement in the quality of life for patients undergoing chemotherapy. Antiemetic therapy has progressed dramatically during the past decade and a half. Fifteen years ago, patients receiving cisplatin for the first time had a median of 12 vomiting episodes within the first 24 hours, whereas now more than 50 percent of such patients have no vomiting episodes at all. Theoretical and clinical challenges remain, however, in the effort to control chemotherapy-induced emesis. The mechanisms of anticipatory vomiting and delayed vomiting are still not understood, and consistently effective therapeutic approaches to these problems have yet to be developed.

Are American children's problems getting worse? A 13-year comparison.

Abstract: Objective To determine whether the prevalence of children's behavioral/emotional problems changed significantly over a 13-year period. Method Problems and competencies reported by parents and teachers for a random sample of 7 to 16 year olds assessed in 1989 were compared with those reported by parents for a 1976 sample and by teachers for a 1981 to 1982 sample. Parent reports were obtained with the Child Behavior Checklist; teacher reports were obtained with the Teacher's Report Form. Results Problem scores were higher and competence scores were lower in 1989 than in the earlier assessments. The secular changes were small but included diverse problems, syndromes, and competencies. Changes did not differ significantly by age, gender, socioeconomic status, nor black/white ethnicity. Correlations of 0.97 to 0.99 between rankings of item scores across 7.5− and 13-year intervals support the stability of the assessment procedures. Despite increases in problem scores, the 1989 U.S. scores were not higher than those in several other cultures. Conclusions Viewed categorically in terms of caseness, more untreated children in the 1989 than the 1976 sample would be considered to need help. Multicohort longitudinal studies now in progress will test predictors of within- and between-cohort change. J. Am. Acad. Child Adolesc. Psychiatry, 1993,32,6:1145–1154.

Nine-Year Outcome of the Vermont Intervention Program for Low Birth Weight Infants

Abstract: Twenty-four low birth weight children who had received an experimental intervention (LBWE) during the neonatal period, 31 control children who had received no treatment (LBWC), and 36 normal birth weight children were compared The intervention involved seven hospital sessions and four home sessions in which a nurse helped mothers adapt to their LBW babies At age 9, LBWE children scored significantly higher than LBWC children on the Kaufman Mental Processing Composite, Sequential, Simultaneous, Achievement, Arithmetic, and Riddles scales, after statistical adjustments for socioeconomic status The LBWE children had also advanced more rapidly in school than had LBWC children Parent (Child Behavior Checklist) and teacher (Teacher's Report Form) ratings of school functioning were more favorable for LBWE than LBWC children, with especially strong effects on Teacher's Report Form scores for academic performance and the attention problems syndrome At age 9, LBWE children were not significantly inferior to normal birth weight children on any measure These results bear out a progressive divergence between the LBWE and LBWC children that first became statistically significant in cognitive scores at age 3 The findings suggest that the intervention prevented cognitive lags among LBW children and that this eventually had a favorable effect on academic achievement, behavior, and advancement in school The progression from no significant differences between LBWE and LBWC children on early cognitive and achievement scores to significant and pervasive differences in later functioning argues for long-term follow-up periods to evaluate properly the power of behavioral interventions to compensate for biological risks

Persistent induction of c-fos and c-jun expression by asbestos.

Abstract: To investigate the mechanisms of asbestos-induced carcinogenesis, expression of c-fos and c-jun protooncogenes was examined in rat pleural mesothelial cells and hamster tracheal epithelial cells after exposure to crocidolite or chrysotile asbestos In contrast to phorbol 12-myristate 13-acetate, which induces rapid and transient increases in c-fos and c-jun mRNA, asbestos causes 2- to 5-fold increases in c-fos and c-jun mRNA that persist for at least 24 hr in mesothelial cells The induction of c-fos and c-jun mRNA by asbestos in mesothelial cells is dose-dependent and is most pronounced with crocidolite, the type of asbestos most pathogenic in the causation of pleural mesothelioma Induction of c-jun gene expression by asbestos occurs in tracheal epithelial cells but is not accompanied by a corresponding induction of c-fos gene expression In both cell types, asbestos induces increases in protein factors that bind specifically to the DNA sites that mediate gene expression by the AP-1 family of transcription factors The persistent induction of AP-1 transcription factors by asbestos suggests a model of asbestos-induced carcinogenesis involving chronic stimulation of cell proliferation through activation of the early response gene pathway that includes c-jun and/or c-fos

Essential nucleotide sequences and secondary structure elements of the hairpin ribozyme.

Abstract: In vitro selection experiments have been used to isolate active variants of the 50 nt hairpin catalytic RNA motif following randomization of individual ribozyme domains and intensive mutagenesis of the ribozyme-substrate complex. Active and inactive variants were characterized by sequencing, analysis of RNA cleavage activity in cis and in trans, and by substrate binding studies. Results precisely define base-pairing requirements for ribozyme helices 3 and 4, and identify eight essential nucleotides (G8, A9, A10, G21, A22, A23, A24 and C25) within the catalytic core of the ribozyme. Activity and substrate binding assays show that point mutations at these eight sites eliminate cleavage activity but do not significantly decrease substrate binding, demonstrating that these bases contribute to catalytic function. The mutation U39C has been isolated from different selection experiments as a second-site suppressor of the down mutants G21U and A43G. Assays of the U39C mutation in the wild-type ribozyme and in a variety of mutant backgrounds show that this variant is a general up mutation. Results from selection experiments involving populations totaling more than 10(10) variants are summarized, and consensus sequences including 16 essential nucleotides and a secondary structure model of four short helices, encompassing 18 bp for the ribozyme-substrate complex are derived.