Siz2 prevents ribosomal dna recombination by modulating levels of Tof2 in Saccharomyces cerevisiae

Abstract

Ribosomal DNA (rDNA) recombination in budding yeast is regulated by multiple converging processes, including posttranslational modifications such as SUMOylation. In this study, we report that the absence of a SUMO E3 ligase, Siz2, results in increased unequal rDNA exchange. Weshow that Siz2 is enriched at the replication fork barrier (RFB) in the rDNA and also controlsthe homeostasis of Tof2 protein.siz2▵ resulted in increased accumulation of total Tof2 in thecell and a consequent increase in the enrichment of Tof2 at the rDNA. Overproducing Tof2 ectopically or conditional overexpression of Tof2 also resulted in higher levels of rDNA recombination, suggesting a direct role for Tof2. Additionally, our chromatin immunoprecipitation(ChIP) data indicate that the accumulation of Tof2 in a siz2▵ mutant resulted in an enhanced association of Fob1, an RFB binding protein at the rDNA at the RFB. This increased Fob1 association at the RFB may have resulted in the elevated rDNA recombination. Our study thus demonstrates that the Tof2 levels modulate recombination at the rDNA.