In haploid cells, double stranded breaks (DSBs) within the rDNA are often initiated by the DNA replication fork-blocking (RFB) activity of Fob1 [22]–[23]. Replication forks traveling opposite to the direction of transcription of the 35S rRNA are blocked by the specific interaction of Fob1 with sequences within the non-transcribed region 1 (NTS1) [24]. This source of DNA replication stress can cause fork collapse to generate DSBs, which can be repaired by homologous recombination to yield a variety of products [25]–[26].
