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M E Levin

Publications and source records attributed to M E Levin.

At least 37 records · Page 2Linked to original sources
PubMed1993

A programmed translational frameshift is required for the synthesis of a bacteriophage lambda tail assembly protein.

Two proteins, one of 31 kDa and one of 16 kDa, are encoded by a segment of the phage lambda tail gene region that contains two overlapping reading frames, neither of which is long enough to encode the larger protein. We show that the abundant 16-kDa protein (gpG) is encoded by the upstream open reading frame, gene G. The 31-kDa protein, gpG-T, is encoded jointly by gene G and the overlapping downstream T open reading frame. gpG-T is synthesized as the result of a translational frameshift that occurs when a ribosome translating the G gene slips back by one nucleotide at a position six codons from the C terminus of the gene and thereby bypasses the G termination codon to continue on in the T open reading frame. The resulting protein shares 135 residues of N-terminal amino acid sequence with gpG, followed by 144 amino acid residues of unique sequence. The frameshift event occurs with a frequency of approximately 4% at the sequence G GGA AAG, which encodes the dipeptide -Gly-Lys- in both the zero and -1 reading frames. The frameshift frequencies of point mutants in this "slippery sequence" argue that codon-anticodon interactions with both the glycyl and the lysyl-tRNA are important for frameshifting to occur. We find no clear evidence for a pausing mechanism to enhance frameshifting, as is seen in other well-characterized frameshifts. No simple secondary structure has been predicted for the region downstream from the slippery sequence, but this downstream sequence does contribute to the frameshifting rate. Our results together with those of Katsura and Kühl show that the frameshift product, gpG-T, has an essential role in lambda tail assembly, acting prior to tail shaft assembly. The role of gpG in tail assembly is not known. We find that both gpG and the gpG-T are absent from mature virions.

Amino Acid Sequence↗
PubMed1993

Mycobacterium smegmatis RNA polymerase: DNA supercoiling, action of rifampicin and mechanism of rifampicin resistance.

We have isolated RNA polymerase from Mycobacterium smegmatis and established conditions for specific transcription initiation in vitro. The M. smegmatis enzyme has a strong dependence on supercoiling of the DNA substrate for transcription from mycobacterial promoters. We also show that RNA polymerase is the target for rifampicin, and that this antibiotic specifically inhibits the transition from synthesis of short oligoribonucleotides to full-length transcripts. RNA polymerase isolated from a rifampicin-resistant mutant of M. smegmatis is less sensitive to rifampicin in vitro, confirming that one mechanism of rifampicin resistance in mycobacteria is through alteration of RNA polymerase. This in vitro transcription system provides a simple method for the characterization of gene expression in mycobacteria including the pathogens Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium leprae. It also provides a system for evaluating potential anti-mycobacterial drugs.

Bacterial Proteins↗
PubMed1993

Does crossing the legs decrease arterial pressure in diabetic patients with peripheral vascular disease?

OBJECTIVE: To evaluate the effect of crossing the legs at the knee and the ankle on peripheral arterial pressures. RESEARCH DESIGN AND METHODS: A prospective study of 6 diabetic patients with known peripheral vascular disease and 5 nondiabetic control subjects without peripheral vascular disease was conducted. Peripheral arterial pressures were taken at the ankle and at the great toe before and after crossing the legs at the knees and ankles. Comparisons were made of measurements obtained in the supine and sitting positions. All crossed leg measurements were taken in the sitting position. RESULTS: Ankle arm indexes and digital arm indexes pressures taken in the sitting position were equal to or higher than supine pressures, with the exception of one subject, GB. In this patient, ankle arm indexes and digital arm indexes on the right extremity were lower in the sitting position, but increased with the legs crossed at the knees and ankles compared with the uncrossed sitting position. In all patients, lower extremity pressures that decreased slightly with crossing the legs remained higher than pressures obtained in the supine position. Statistical analyses showed no significant differences. Wave forms did not change even when there was a slight decrease in ankle arm indexes or digital arm indexes. Control subjects without peripheral vascular disease showed no change in pressures with crossing the legs. CONCLUSIONS: Crossing the legs at the knees and ankles does not result in a significant decrease in peripheral arterial pressures in diabetic patients with peripheral vascular disease.

Analysis of Variance↗
PubMed1992

Subtractive processes in light adaptation.

We measured the time course of light adaptation in foveal vision following the onset of an adapting background. Several adaptational steps in the low to mid photopic range were examined. The time course of multiplicative and subtractive components of the adaptation were extracted from the data. Unlike previous findings there were no subtractive changes for several hundred milliseconds following light onset, and the process took 10-15 sec to reach steady state. It seems likely that the fast component previously observed results from effectively instantaneous center-surround antagonism, and that our measurements reflect a second subtractive process involving the slow loss of the d.c. signal over time.

Adaptation, Ocular↗
PubMed1987

Understanding your diabetic patient.

In 1987, it is quite evident that the diagnosis etiology, complications, and management of diabetes have come a long way since those days 65 years ago when the lifespan of an insulin-requiring diabetic was 1.2 years. There are exciting times ahead. Today, with the number of diabetics increasing and the problems multiplying, anyone caring for diabetics should have a general knowledge of all aspects of the disease and be able to participate in the total care of the diabetic. For example, the podiatrist should not confine diabetic care only to the foot, but should check blood sugars and blood pressures, take brief diabetic histories, suggest yearly eye examinations, and encourage adherence to diet, blood sugar control, exercise programs, and the avoidance of smoking. While great strides have been made in diabetic management particularly in the last decade, the ultimate cure is yet to be achieved and is the goal of the future.

Adult↗
PubMed1986

Pregnancy and diabetes. Team approach.

Each year, 10,000 babies are born to diabetic women. Gestational diabetes occurs in 2% of all pregnant women, resulting in 60,000 to 90,000 cases of gestational diabetes yearly. Prior to 1922 and the discovery of insulin, fetal mortality for the pregnant diabetic was almost 100%. Today, total fetal mortality for the pregnant and gestational diabetic is approaching that of the nondiabetic. This has been achieved by extremely tight control of blood glucose levels throughout pregnancy, with blood glucose levels averaging under 100 mg/dL/day and glycosylated hemoglobin levels in the normal range throughout pregnancy. An increased number of malformations in fetuses of pregnant diabetic women is still a problem. However, animal and human studies indicate that a normal level of glycosylated hemoglobin at conception may significantly reduce these malformations.

Birth Weight↗
PubMed1980

The diabetic foot.

Explore the source record for details and available documents.

Amputation, Surgical↗
PubMed1978

Effects of hypoglycemic agents on vascular complications in patients with adult-onset diabetes. VII. Mortality and selected nonfatal events with insulin treatment.

The University Group Diabetes Program is a long-term prospective clinical trial designed to evaluate the effects of various hypoglycemic agents on vascular complications in patients with asymptomatic adult-onset diabetes. Mortality and blood glucose levels were determined as well as certain nonfatal events for patients assigned to diet alone or to either of two insulin treatment regimens. Lower levels of blood glucose with mean values close to normoglycemia were achieved in the treatment group in which the insulin dosage was adjusted to achieve normoglycemia compared with the levels achieved in patients treated with diet alone or with a fixed dose of insulin. In spite of differences in blood glucose levels among the treatment groups, there were only minor differences in the occurrence of fatal or nonfatal events.

Blood Glucose↗
PubMed1976

Effects of diabetes mellitus on bone mass in juvenile and adult-onset diabetes.

To assess the influence of diabetes mellitus on bone metabolism, we measured skeletal mass in the forearms of 35 patients with juvenile diabetes on insulin and 101 stable patients with adult-onset diabetes, on diet alone, insulin, or oral hypoglycemic agents. There was a significant loss of bone mass in both juvenile and adult-onset diabetes (P less than 0.01) as compared to controls matched for age and sex. The decrease was already present in patients with diabetes of less than five years' duration. Bone loss and duration of the diabetes did not correlate; the greatest decrease in bone mass was observed in the patients receiving oral agents. These data are consistent with the hypothesis that the loss of skeletal tissue in diabetes reflects the underlying disease since it occurs early and is not related to severity as evidenced by the need for insulin, to duration, or to treatment with insulin or diet alone.

Adult↗