Depression of thymine dimer excision in various excision-proficient strains of Escherichia coli

Persistence of thymine dimers in the replicated DNA of Escherichia coli B/r Hcr+

“…In our previous experiments E. coli B/r Hcr ÷ cells irradiated by a dose dimerizing 0.15% of thymine exhibited complete excision in the exponentially growing culture [11 ] and an almost complete depression of excision in the prestarved culture [8,7]. In the experiments described here depression of dimer excision was less pronounced, probably due to different conditions (growth in heavy medium with a low level of glucose, transfer to light medium).…”

“…More recently we have shown that a simultaneous starvation for thymine and amino acid (AA-T-) applied prior to u.v. irradiation leads to depression of thymine dimer excision in various excision-proficient strains of Escherichia coli when proper starvation conditions are employed [7]. We have also shown that the starvation need not cause either death of cells during the treatment or a decrease of surviving ability [8,7].…”

Evidence that dimers remaining in preinduced Escherichia coli B/r Hcr+ become insensitive after DNA replication to the extract from Micrococcus luteus

“…Rather inconsistent with this, however, excision repair was found to be inhibited by a foregoing induction. This has been observed with Weigle reactivation of phage X (Boyle and Setlow, 1970), as well as with Chinese hamster cells exposed separately to N-acetoxy-2-acetylaminofluorene and UV (Ahmed and Setlow, 1977); this has also been observed in wild type bacterial cells namely, E. coli B/r Hcr+, E. coli K-12 AB 2497, and E. coli 15 555-7 preinduced by thymine starvation (Sedliakova et al, 1974) as well as in E. coli B/r Hcr+ (Sedliakova' et al, 1978a), E. coli WP2, and E. coli 15 555-7 preinduced by UV preinduction but not in UV-preinduced E. coli K-12 AB 2497(Sedliakova et al, 1980a or in thymineless preincubated M. radiodurans (Budayov'a and Sedliakova', 1977). The data presented in this paper provide evidence that in wild type cells a UV-inducible repair pathway operates that enables tolerating lesions to remain unexcised.…”

“…coli B/r Hcr+ cells, unlike mammalian cells, perform efficient dimer excision when irradiated in the exponential phase of growth. If, however, before UV irradiation, they are exposed to thymine starvation (Sedliakova' et al, 1974) and/or irradiated by a nonlethal UV predose (Sedliakova et al, 1978a), they behave like mammalian cells, leaving numerous dimers unexcised. The present study has been designed to elucidate the fate of dimers remaining in E. coli B/r Hcr+ irradiated with inducing and lethal fluences.…”