Formation of single-stranded breaks in newly-synthesized Escherichia coli DNA following treatment with bleomycin
Dzhataev, S.A.; Tanirbergenov, T.B.; Tarasov, V.A.
Genetika 16(4): 733-735
1980
ISSN/ISBN: 0016-6758 PMID: 6160080 Document Number: 162329
Changes in molecular weight of newly synthesized DNA was studied after bleomycin treatment of Escherichia coli cells. The treatment by this drug causes only the increase of dispersion in sedimentation profiles of daughter DNA strands in wild type cells. There are two alternative explanation of this fact. First, single-strand breakage does not occur in newly synthesized DNA, i.e. bleomycin-induced athyminic sites do not block cellular DNA polymerases. Second, it is possible to explain it by quick rejoining of given breaks by cell repair systems. The sedimentation profile of daughter DNA strands of recA mutant rules out the first possibility. Observed shift to low molecular weight fractions region strongly indicates the formation of single-strand breaks in newly synthesized DNA. Extensive daughter DNA degradation in xthA mutant supports the idea of the existence of very effective excision repair in the case of apyrimidinic sites. Thus, non-eliminated bleomycin-induced damage causes the formation of single-strand breaks in newly synthesized DNA strands. These breaks may be repaired in the course of recA-dependent post-replication repair.