Methods designed for the identification and characterization of in vitro and in vivo chromatin assembly mutants in Saccharomyces cerevisiae

Assembly of DNA into chromatin allows for the formation of a barrier that protects naked DNA from protein and chemical agents geared to degrade or metabolize DNA. Chromatin assembly occurs whenever a length of DNA becomes exposed to the cellular elements, whether during DNA synthesis or repair. This report describes tools to study chromatin assembly in the model system Saccharomyces cerevisiae. Modifications to an in vitro chromatin assembly assay are described that allowed a brute force screen of temperature sensitive (ts) yeast strains in order to identify chromatin assembly defective extracts. This screen yielded mutations in genes encoding two ubiquitin protein ligases (E3s): RSP5, and a subunit of the Anaphase Promoting Complex (APC), APC5. Additional modifications are described that allow for a rapid analysis and an in vivo characterization of yeast chromatin assembly mutants, as well as any other mutant of interest. Our analysis suggests that the in vitro and in vivo chromatin assembly assays are responsive to different cellular signals, including cell cycle cues that involve different molecular networks.