Novel Regulatory Properties of Saccharomyces cerevisiae Arp4

the macrolide antibiotic rapamycin. We show the changes of mRNA levels of selected genes under these conditions. The upregulation of stress genes as a consequence of treatmentwithrapamycinwaslargelyMsn2p/Msn4p-dependent.Thesensitivitytowards rapamycin indicates a participation of Arp4 in the regulation of the TOR pathway. Consistently, arp4G161D cells exhibited an affected cell cycle. Long-term cultivation, which leads to a G1 arrest in wild-type cells, provoked arrest in G2/M (more than 60%) in the mutant strain. The same effect was observed upon treatment with rapamycin, indicating an unexpected relationship of Arp4 to TOR-mediated cell cycle arrest.