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M S Tang

Publications and source records attributed to M S Tang.

44 records · Page 3Linked to original sources
PubMed1982

Reevaluation of a DNA binding activity with specificity for chemically modified DNA.

A DNA binding activity which appeared in direct filter binding assays to show specificity for DNA modified by N-acetoxy-2-acetylaminofluorene (AAF), N-methyl-N-nitrosourea and methylmethanesulfonate (Moranelli and Lieberman, Proc. Natl. Acad. Sci. USA 77, 3201, 1980) has been further purified and characterized. Equilibrium competition binding experiments indicate this activity shows little, or no, preferential binding of AAF-modified DNA compared to single-stranded DNA and only a small preference compared to u.v.-irradiated DNA or double-stranded DNA. These findings demonstrate the difficulty of using direct filter binding assays when purifying proteins with a desired biological function and the need to perform competition assays when evaluating specificity.

2-Acetylaminofluorene↗
PubMed1981

The effects of lexA101, recB21, recF143 and uvrD3 mutations on liquid-holding recovery in ultraviolet-irradiated Escherichia coli K12 recA56.

Using an Escherichia coli K12 recA strain, we have tested the effects of incorporating additional mutations affecting deoxyribonucleic acid (DNA) repair on ultraviolet-radiation sensitivity and on the expression of liquid-holding recovery (LHR). (This laboratory had previously shown that a mutation at uvrA, uvrB or uvrC blocked LHR in a recA strain.) In the recA56 background, an additional lexA101 mutation had no effect on UV-radiation sensitivity or LHR. The addition of a recB21 mutation to recA56 did not alter UV-radiation sensitivity, but greatly increased the rate of LHR. The recB gene product (exonuclease V) appears to act as a competitive inhibitor both of excision repair and of photoreactivation under liquid-holding (LH) conditions. The uvrD3 mutation increased the radiation sensitivity of a recA strain, and almost completely blocked LHR. The recA uvrD strain showed more DNA degradation and DNA double-strand breaks during LH than did the recA strain. The recF143 mutation increased both UV-radiation sensitivity and LHR in a recA strain, suggesting that the recF gene product may also function in recA-independent pathways of DNA repair.

DNA Repair↗
PubMed1980

Coordination between chromosome replication and cell division in Escherichia coli.

Cell division properties of Escherichia coli B/r containing either a dnaC or a dnaI mutation were examined. Incubation at nonpermissive temperature resulted in the eventual production of cells of approximately normal size, or slightly smaller, which lacked chromosomal DNA. The cell division patterns in cultures which were grown at permissive temperature and then shifted to nonpermissive temperature were consistent with: first, division and equipartition of chromosomes by cells which were in the C and D periods at the time of the shift; second, an apparent delay in cell division; and third, commencement of the formation of chromosomeless cells. In glucose-grown cultures of the dnaI mutant, production of chromosomeless cells continued for at least 120 min, whereas in the dnaC mutant chromosomeless cells were formed during a single interval between 110 and 130 min after the temperature shift. The results are discussed in light of the hypothesis that replication of a specific chromosomal region is not an obligatory requirement for the initiation and completion of the processes leading to division in a cell which contains at least one functioning chromosome.

Cell Division↗