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Biomedical subjects

B Weiss

Publications and source records attributed to B Weiss.

At least 361 records · Page 20Linked to original sources
PubMed1977

Transient accumulation of Okazaki fragments as a result of uracil incorporation into nascent DNA.

Strains of Escherichia coli with a mutation in the sof (dnaS) locus show a higher than normal frequency of recombination (are hyper rec) and incorporate label into short (4-5S) DNA fragments following brief [3H]thymidine pulses [Konrad and Lehman, Proc. Natl. Acad. Sci. USA 72, 2150 (1975)]. These mutant strains have now been found to be defective in deoxyuridinetriphosphate diphosphohydrolase (dUTPase; deoxyuridinetriphosphatase, EC 3.6.1.23), the enzyme that catalyzes the hydrolysis of dUTP to dUMP and PPi. Reversion of one sof- mutation to sof+ restores dUTPase activity and abolishes the accumulation of labeled 4-5S DNA fragments. Mutants initially isolated as defective in dUTPase (dut-) are also hyper rec and show transient accumulation of short DNA fragments. Both the sof and dut mutations are located at 81 min on the E. coli map, closely linked to the pyrE locus. The sof and dut loci thus appear to be identical. A decrease in dUTPase as a consequence of a sof or dut mutation may result in the increased incorporation of uracil into DNA. Rapid removal of the uracil by an excision-repair process could then lead to the transient accumulation of short DNA fragments. It is possible that at least a portion of the Okazaki fragments seen in wild-type cells may originate in this way.

Chromosome Mapping↗
PubMed1977

III. Covalent coupling of rat liver phenylalanine hydroxylase.

Optimal conditions have been determined for the coupling of rat liver phenylalanine hydroxylase (PheH) to activated CH-Sepharose-4B. When 12 mg of ligand was reacted with 100 mg of matrix, 20% of the initial enzyme activity was covalently bound along with 55% of the protein. The coupled enzyme showed greater thermal stability from 50 degrees to 60 degrees after heating for 15 min, a lower optimum pH, 5.8, slightly less inhibition by Ag+, Cu+2, and Hg+2, and greater resistance to hydrolysis by alpha-chymotrypsin and protease. The uncoupled enzyme, however, exhibited greater storage stability than the covalently linked enzyme at 25 degrees after 24 hrs and at 0 degrees after 21 days. Alteration of the microenvironment by the introduction of sulfhydryl groups and positive and negative charged carriers during coupling of the enzyme either had no effect or markedly reduced hydroxylase activity.

Animals↗
PubMed1976

Needle puncture of fetus: a complication of second-trimester amniocentesis.

Needle puncture of the fetus has rarely been reported with midtrimester amniocentesis. This paper contains the report of five cases of needle scars in infants born after second-trimester amniocentesis for prenatal diagnosis of fetal genetic disorders. Since this complication may be more frequent than has been previously believed, there is the possibility that damage to the fetus may occur. It is suggested that the products of all abortions and all live-born and stillborn infants delivered following amniocentesis should be examined for evidence of injury.

Amniocentesis↗
PubMed1976

[The treatment of ptyalism in children with cerebral lesions (author's transl)].

The cytotoxic and alkylating substance, mustard gas, causes both acute poisoning and also damage to numerous organs following chronic exposure. Especially important is the carcinogenic effect, also confirmed in humans. 34 years after occupational exposure to mustard gas with many intoxication episodes, a former munition-worker died of a glioblastoma; two years before his death a neurofibroma was detected in the thorax and removed by operation. The causal connection between the mustard gas exposure and the development of two neurogenic tumors rests on the statistically significantly raised frequency of malignant tumors and the established psychic changes in former workers with mustard gas and especially on the production of malignant tumors of the central nervous system in experimental animals with alkylating nitrosamines.

Aged↗
PubMed1976

Endonuclease II of Escherichia coli is exonuclease III.

Exonuclease III, a phosphatase-exonuclease specific for bihelical DNA, wn the preparation was endonuclease II, an activity specific for DNA that has been partially depurinated by treatment with methyl methanesulfonate. The two activities, which could not be separated by electrophoresis, by sedimentation, or by gel filtration, were associated with a single monomeric protein of 28,000 daltons. To explain how a relatively small protein could have such diverse activities, it is proposed that one site on the enzyme can recognize interstrand spaces created either by depurination or by spontaneous terminal unwinding of a DNA duplex.

Deoxyribonucleases↗
PubMed1976

Genetic mapping of xthA, the structural gene for exonuclease III in Escherichia coli K-12.

The genes xthA, pncA, and pabB were ordered relative to others by two- and three-factor transductional crosses with bacteriophage P1. The genes studied span 2 min (2%) of the genetic map of Escherichia coli K-12 in the clockwise sequence pheS-pfkB-xthA-pncA-gap-pabB-fadD. Eleven independently derived xth mutations were examined; all were known to affect exonuclease III and its associated endonuclease II activity, and all were mapped in the xthA region. pncA mutations were found to confer resistance to 6-aminonicotinamide, whereas some pheS mutations are known to specify resistance to p-fluorphenylalanine. xth mutations were readily transferred into other strains by selecting for these co-transducible drug resistance markers.

6-Aminonicotinamide↗