RSC2, Encoding a Component of the RSC Nucleosome Remodeling Complex, Is Essential for 2μm Plasmid Maintenance in Saccharomyces cerevisiae

The stable maintenance of the 2μm circle plasmid depends on its ability to overcome intrinsic maternal inheritance bias, which in yeast normally results in the failure to transmit DNA molecules efficiently to daughter cells. In addition to the plasmid proteins Rep1 and Rep2 acting on the plasmid DNA locus STB, it is likely that other chromosomally encoded yeast proteins are required. We have isolated mutants of yeast unable to maintain 2μm and found that RSC2 is essential for 2μm to overcome maternal inheritance bias. Rsc2 is part of a multisubunit RSC chromatin remodeling complex, and we show that in the absence of Rsc2 the chromatin structure of the STB region is significantly altered and the Rep1 protein loses its normal localization to subnuclear foci. Rsc1, a closely related homolog of Rsc2 present in an alternative form of the RSC complex, is not required for 2μm maintenance and does not replace the requirement for Rsc2 when overexpressed. This represents the first specific role for Rsc2 that has been related to a change in chromatin structure, as well as the first direct evidence linking chromatin structure to 2μm segregation.