Аннотация:Genome in vivo is constantly exposed to the damaging effects of the environment. Single-strand breaks (SSBs) are the most fre- quently occurring DNA lesions. Accumulation of unrepaired SSBs can interfere with the cells metabolism and increase geno- mic instability. In vivo, SSBs are repaired in specific pathway, but, in eukaryotic nuclei, DNA is organized in chromatin that could affect the accessibility of lesions to sensor proteins. Breaks in a template strand induce arrest of RNA polymerase II (PolII) in vitro and in vivo and can be revealed in a transcription-depen- dent manner.
Our recent biochemical studies identified two key intermedi- ates formed during transcription through a nucleosome by RNAP that are nearly homogeneous, active and stable by bio- chemical criteria (complexes stalled after entering 24 or 42 bp into the nucleosome; EC+24 or EC+41, respectively).