130 Transcription blockage by single-strand breaks in various sequences and the general model for transcription blockage by R-loop formation

Transcription blockage can strongly affect gene expression and trigger other important biological phenomena like transcription-coupled repair (Hanawalt & Spivak, 2008). Thus, it is of interest to study the various factors that can cause transcription blockage and to elucidate mechanisms of their action. We studied T7 RNA polymerase (T7 RNAP) transcription blockage caused by single-stranded breaks localize either in the template or the nontemplate DNA strand (Belotserkovskii et al., 2013; Neil, Belotserkovskii, & Hanawalt, 2012). Partial T7 RNAP blockage was observed in both cases, but the patterns of blockage signals differed dramatically for these two types of lesions. A break in the template strand produces a sharp predominant blockage signal corresponding to the position of the break, as expected for an interruption in the DNA strand that is continuously tracked by RNAP during transcription. In contrast, a break in the nontemplate strand produces an irregular ladder of weak blockage signals that begins...