Distinct associations of the Saccharomyces cerevisiae Rad9 protein link Mac1-regulated transcription to DNA repair.

While it is known that ScRad9 DNA damage checkpoint protein is recruited to damaged DNA by recognizing specific histone modifications, here we report a different way of Rad9 recruitment on chromatin under non DNA damaging conditions. We found Rad9 to bind directly with the copper-modulated transcriptional activator Mac1, suppressing both its DNA binding and transactivation functions. Rad9 was recruited to active Mac1-target promoters (CTR1, FRE1) and along CTR1 coding region following the association pattern of RNA polymerase (Pol) II.

Synergy of Hir1, Ssn6, and Snf2 global regulators is the functional determinant of a Mac1 transcriptional switch in S. cerevisiae copper homeostasis.

To gain insights on the transcriptional switches that modulate proper copper homeostasis in yeast, we have examined in detail functional interactions of the relevant transcriptional activator Mac1. We identified Hir1 transcriptional repressor and histone chaperone as a Mac1-interacting protein. This association directly recruits Hir1 on a Mac1 target, CTR1 promoter, quantitatively under induction conditions.

Rad9 interacts with Aft1 to facilitate genome surveillance in fragile genomic sites under non-DNA damage-inducing conditions in S. cerevisiae.

DNA damage response and repair proteins are centrally involved in genome maintenance pathways. Yet, little is known about their functional role under non-DNA damage-inducing conditions. Here we show that Rad9 checkpoint protein, known to mediate the damage signal from upstream to downstream essential kinases, interacts with Aft1 transcription factor in the budding yeast.

Nhp6 facilitates Aft1 binding and Ssn6 recruitment, both essential for FRE2 transcriptional activation.

We found Nhp6a/b yeast HMG-box chromatin-associated architectural factors and Ssn6 (Cyc8) corepressor to be crucial transcriptional coactivators of FRE2 gene. FRE2 encoding a plasma membrane ferric reductase is induced by the iron-responsive, DNA-binding, transcriptional activator Aft1. We have shown that Nhp6 interacts directly with the Aft1 N-half, including the DNA-binding region, to facilitate Aft1 binding at FRE2 UAS.