A genetic assay for monitoring epigenetic activity in yeast.

Elg1 is a conserved RFC (replication factor C)-like protein essential for genome stability via its PCNA unloading activity following DNA replication. Besides the role of PCNA in increasing the processivity of DNA polymerase, it is indispensable for replication-coupled nucleosome assembly. The lack of Elg1 protein leads to PCNA retention on replicated DNA, which eventually results in genome instability and heterochromatin de-silencing due to inefficient nucleosome assembly.

Here, we are using a Cre- loxP based assay (CARSH) to quantitatively measure the effect of Elg1 and its genetic interactors on the heterochromatin silencing at the silenced mating-type locus of Saccharomyces cerevisiae. We observed the effect of different Elg1 mutants on the heterochromatin silencing. We find that the Elg1 ATPase domain is essential for maintaining heterochromatin silencing at the HML locus. We are currently studying the effect on the CRASH assay by mutating additional genes that interact with Elg1.