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Biomedical subjects

C Counsilman

Publications and source records attributed to C Counsilman.

3 recordsLinked to original sources
PubMed1981

Sensitivity and resistance of human melanoma cells to ultraviolet radiation.

A human melanoma cell line (MM253) was found to be sensitive to ultraviolet (UV) radiation, having a Do of 1.0 J/M2 when cloned on plastic culture dishes and a Do of 2.3 J/m2 when cloned in agar. These figures are much lower than those obtained for all other human melanoma cell lines studied in this laboratory (Do of 32-40 J/m2) and demonstrate that MM253 is unusually UV sensitive. The increased level of UV sensitivity in MM253 is not due to a reduced capacity for excision of pyrimidine dimers, repair of DNA single-strand breaks or elongation of newly-synthesized DNA strands when comparison is made with a UV-resistant melanoma cell line.

Cell Line↗
PubMed1976

A mammalian nicking endonuclease.

Purification and properties are described for an endonuclease isolated from calf thymus which attacks double-stranded, unmodified DNA, primarily by making single-strand breaks. No detectable acid-soluble products arise from the reaction. Double-strand breaks may occasionally be produced by the introduction of single-strand breaks on opposite strands in close proximity. The enzyme does not attack denatured DNA and is not inhibited by tRNA. Although added divalent cations are not required for activity, the enzyme is inhibited by EDTA, which suggests an essential role for bound cations; reaction is inhibited by Ca2+. The endonuclease has a broad pH optimum and is inactivated by preincubation at temperatures of 45 degrees C and higher. The molecular weight as determined by gel chromatography is about 30 000. Analysis of the products of reaction on a defined substrate, bacteriophage T3 DNA, by sedimentation in alkaline sucrose density gradients indicates limit products with chain lengths of about 0.8 X 10(6) daltons. On electrophoresis in agarose gels these products were shown to be heterogeneous in size. The endonuclease appears to generate 3'-hydroxyl and 5'-phosphate ends. The ability of the endonuclease to utilize bovine DNA as substrate argues against a restriction role for this enzyme.

Animals↗