Anc1 : a new player in the cellular response to DNA damage

Abstract

The continuity of living organisms depends on their ability to protect their genomes from a constant assault by internal and external sources of damage. To this end, cells have developed a variety of mechanisms to avoid and repair damage to their genetic material. In this thesis, we analyze a yeast gene that has a previously uncharacterized role in the cell's ability to survive after DNA damage. This gene, ANC1, is interesting for several reasons. First, ANC1 is the only common member of seven different multiprotein complexes that all function in general RNA polymerase II-mediated transcription. Second, ANC1 is evolutionarily well-conserved between yeast and humans, suggesting that its function is critically important for survival. And finally, three out of four human homologs of ANC1 have a role in the MLL gene fusions associated with human acute leukemias. Here, we show that ANC1 falls into the same genetic pathway as several members of the postreplication repair (PRR) pathway, but has additive or synergistic relationships with other members of the pathway. Based on our epistasis data and our analysis of ANC1's role in mutagenesis, ANC1 functions in the error-free branch of PRR. Genetically, however, ANC1 is not in the same pathway as several canonical error-free branch members, and thus defines a new error-free branch of PRR. Similar to other genes involved in error-free PRR, ANC1 was found to have a role in suppressing the expansion of the Huntington's Disease-associated CAG triplet repeat. Additionally, we demonstrate a role for ANC1 in the global transcriptional response to MMS treatment: expression changes in transcripts regulated in response to environmental stress are significantly abrogated in ANC1 cells.

(cont.) The regulation of this transcriptional response to environmental stress has previously been attributed to the Mec1 signaling pathway. To determine if ANC1's effect on global transcription is linked to Mec1signaling, we assayed the role of ANC1 in mediating the protein-level DNA damage response of Sml1, a downstream member of the Mec1 pathway. We observed that in the presence of MMS the Sml1 protein is abnormally degraded in ANC1 cells, indicating a possible role for ANC1 in this pathway.