In eukaryotes, ribosomal genes (rDNA) are organized in tandem repeats localized in one or a few clusters. Each repeat encompasses a transcription unit and a non-transcribed spacer. Replication forks, which move in the opposite direction to transcription, stop at specific sites called “replication fork barriers” (rRFBs), in the non-transcribed spacer close to the 3’ end of the transcription unit.
Although this blocking of the forks is conserved through evolution, the proteins responsible are different for different species.
The work published in Nucleic Acids Research by Dr. Schvartzman’s group studies blocking of the replication forks in the rDNA of Saccharomyces cerevisiae (the bread yeast), which depends on the Fob1 protein. Experiments have shown that DNA sequences adjacent to Fob1 protein binding sites, as well as the relative abundance of this protein, modulate the efficiency of rRFBs to block the progress of replication forks.
Reference: The abundance of Fob1 modulates the efﬁciency of rRFBs to stall replication forks. Alicia Castán, Pablo Hernández, Dora B. Krimer, Jorge B. Schvartzman. Nucleic Acids Research, 2017. DOI: 10.1093/nar/gkx655
[Image: adapted from Nucleic Acids Research]