[Sister chromatid exchanges following incorporation of bromine into cytosine DNA nucleotides. I. Combined use of 5-bromdeoxycytidine and thymidine for the purpose of incorporating bromine into DNA cytosine]

Abstract

In the cultured in vitro human blood lymphocytes treated with 5-bromodeoxycytidine (BrdC) plus thymidine (dT) in concentrations of 0.05 mM and 0.4 mM, respectively, metaphases of the second division, containing chromosomes with differentially stained sister chromatids appear after a 30 hours treatment, attaining 85 per cent at 36 hours. Under the treatment with BrdC or BrdU alone, the similar percentage of metaphases is observed at 28 hours. Similar results are obtained if, at 16--18 hours, the culture medium, containing BrdC plus dT is either replaced with a medium free of both the precursors, or supplied once more vith (0.05 mM) or dC(0.05 mM). The The observed slowing movement of cells through out the cell cycle, due to the treatment with BrdC plus dT, is explained by the inhibitory effect of dT on DNA synthesis which is manifested as BrdC catabolism. It is concluded that BrdC administered together with the cell cycle-slowing doses of thymidine is predominantly incorporated into cytosine of DNA.