Mcm1p binding sites in ARG1 positively regulate Gcn4p binding and SWI/SNF recruitment

Transcription of the arginine biosynthetic gene ARG1 is activated by Gcn4p, a transcription factor induced by starvation for any amino acid. Previously, we showed that Gcn4p binding stimulates the recruitment of Mcm1p and co-activator SWI/SNF to ARG1 in cells via Gcn4p induction through amino acid starvation. Here, we report that Gcn4p binding is reduced by point mutations of the Mcm1p binding site and increased by overexpression of Mcm1p. This result suggests that Mcm1p plays a positive role in recruiting activator Gcn4p to ARG1, similar to the previously described cooperative interaction of Mcm1p with sequence-specific transcription factors at their promoters. In addition, the mutational analysis of Mcm1p binding sites showed that recruitment of the co-activator SWI/SNF correlated more closely with binding of Mcm1p than of Gcn4p at ARG1. Consistent with this, SWI/SNF co-immunoprecipitated with Mcm1p, but not with Gcn4p. These results support that Mcm1p increases the SWI/SNF recruitment at ARG1, a Gcn4p target promoter. The interaction between Mcm1p and SWI/SNF was abolished in a snf2 deletion strain containing an intact SWI/SNF sub-complex, suggesting that Mcm1p targets the catalytic subunit, which has ATPase activity, during SWI/SNF recruitment. We propose that Mcm1p contributes to active transcription at the ARG1 promoter by increasing the binding of the activator Gcn4p and by recruiting the co-activator complex SWI/SNF at ARG1 under Gcn4p-induced conditions.