Novel connections between DNA replication, telomere homeostasis and the DNA damage response revealed by a genome-wide screen for <italic>TEL1/ATM</italic> interactions in <italic>Saccharomyces cerevisiae</italic>

Abstract

Tel1p is the budding yeast ortholog of the mammalian tumor suppressor and DNA damage response (DDR) kinase ATM. However, <italic>tel1-δ</italic> cells, unlike <italic>ATM</italic>-deficient cells, do not exhibit sensitivity to DNA damaging agents, but do display shortened (but stably maintained) telomere lengths. Neither the extent to which ATM/Tel1p functions in the DDR nor the mechanism by which ATM/Tel1p contributes to telomere metabolism is well-understood. In this dissertation, I present our large-scale transcriptional profiling of normal and <italic>ATM</italic>-deficient lymphoblast cell lines in response to ionizing radiation (IR). From these results, we make the surprising observation that <italic>ATM</italic>-deficient cells exhibit no significant defects in IR-induced gene expression, which along with work from others suggests that significant redundancy exists in the DNA damage response, and may be an explanation for the relative DNA damage insensitivity in <italic>tel1-δ</italic> yeast cells. To address this question, I performed a comprehensive genome-wide screen for genetic interactions with <italic>tel1-δ</italic> that cause sensitivity to MMS and/or ionizing radiation, along with follow-up characterizations of the 13 interactions yielded by this screen. Surprisingly, many of the <italic>tel1-δ</italic> interactions that confer DNA damage sensitivity also exacerbate the short telomere phenotype, suggesting a connection between these two phenomena. Restoration of normal telomere length in the <italic>tel1-δ</italic> <italic>xxx-δ</italic> mutants results in only minor suppression of the DNA damage sensitivity, demonstrating that the sensitivity of these mutants must also involve mechanisms independent of telomere length. In support of a model for increased replication stress in the <italic>tel1-δ</italic> <italic>xxx-δ</italic> mutants, I show that depletion of dNTP pools through pre-treatment with hydroxyurea renders <italic>tel1-δ</italic> cells (but not wild-type) MMS-sensitive, demonstrating that under certain conditions, Tel1p does indeed play a critical role in the DDR.