The selfish yeast plasmid exploits a SWI/SNF-type chromatin remodeling complex for hitchhiking on chromosomes and ensuring high-fidelity propagation
Extra-chromosomal selfish DNA elements can evade the risk of being lost at every generation by behaving as chromosome appendages, thereby ensuring high fidelity segregation and stable persistence in host cell populations. The yeast 2-micron plasmid and episomes of the mammalian gammaherpes and papilloma viruses that tether to chromosomes and segregate by hitchhiking on them exemplify this strategy. We document for the first time the utilization of a SWI/SNF type chromatin remodeling complex as a conduit for chromosome association by a selfish element. One principal mechanism for chromosome tethering by the 2-micron plasmid is the bridging interaction of the plasmid partitioning proteins (Rep1 and Rep2) with the yeast RSC2 complex and the plasmid partitioning locus STB. We substantiate this model by multiple lines of evidence derived from genomics, cell biology and in vivo and in vitro interaction analyses. We describe a Rep-STB bypass system in which a plasmid non-covalently associated with the RSC complex mimics segregation by chromosome hitchhiking. Given the ubiquitous prevalence of SWI/SNF family chromatin remodeling complexes among eukaryotes, it is likely that the 2-micron plasmid paradigm or analogous ones will be encountered among other eukaryotic selfish elements. Overall design: Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) and Cleavage Under Targets and Tagmentation (CUT&Tag) sequencing for the partitioning proteins Rep1, Rep2 and controls in wild-type (wt) and rsc2 mutant strains of yeast Saccharomyces cerevisiae