ИСТИНА

Single strand breaks (SSBs) are incontinuities in the DNA backbone that often include damaged 3’ and 5’ termini surrounding the break. They are frequently caused by reactive oxygen species, which can disintegrate backbone sugars by direct attack, and represent the prevalent form of endogenous DNA damage in living cells. SSBs in template strand (TS-SSBs) of a transcribed sequence are shown to be bypassed during transcription in vitro by different RNA polymerases (RNAP), at efficiencies varying significantly depending on the 5’ and 3’ backbone end-chemistries at the break and the presence or absence of adjacent abasic sites. RNA polymerase from Escherichia coli have been shown to efficiently bypass a single abasic site in the template DNA but to stop at SSBs with an adjacent single nucleotide gap. The effect of SSB itself on E. coli RNAP elongation was not yet investigated. In the present work the effect of TS-SSBs on elongation by E. coli RNAP was studied using the experimental system developed earlier. Templates with randomly or uniquely introduced TS-SSBs were transcribed in vitro by E. coli RNAP. Efficiency of elongation through the lesion and enzyme stalling were evaluated.