ИСТИНА

Transcription through nucleosomes by RNA polymerases (RNAP) is accompanied by formation of small intranucleosomal DNA loops containing the enzyme (i-loops). These i-loops form much more efficiently in the presence of single-strand DNA breaks in a non-template DNA strand (NT-SSBs) and induce arrest of transcribing RNAP [1], thus allowing detection of the damages by the enzyme. The structure of transcription intermediate containing i-loop was studied using biochemical approaches and electron microscopy [2]. It was shown, that after RNAP passes the damage, the enzyme can backtrack, and DNA behind it recoils on the surface of the histone octamer, forming an i-loop that locks RNAP in the arrested state. Our newly obtained data suggests an important role of N-terminal tails of core histones in formation of i-loops during transcription of promoter-proximal region of the nucleosomal DNA (in press). Since the i-loops are formed much more efficiently in the presence of SSBs positioned behind the transcribing enzyme, the loops likely play a role in transcription-coupled repair of DNA damages hidden in chromatin structure. [1] Pestov N.A. et. al., Science Advances 1, e1500021 (2015). [2] Gerasimova N.S. et. al., Cells 11(17), 2678 (2022).