Gln3 Mutations Dissociate Responses to Nitrogen Catabolite Repression and Rapamycin Inhibition of TorC1

Abstract

The GATA‐family transcription activator, Gln3 responds to the cell's nitrogen requirements and environmental resources. In nitrogen excess (YNB‐Gln medium), Gln3 is sequestered in the cytoplasm and the transcription it mediates is minimal. In contrast, during nitrogen‐limitation (YNB‐Pro), Gln3 relocates to the nucleus and activates transcription of genes required to scavenge poor nitrogen sources; these responses are designated nitrogen catabolite repression (NCR). Since rapamycin (Rap) addition also elicits nuclear Gln3 localization [Rap is an inhibitor of the global regulator TorC1], TorC1 has been thought to be responsible for NCR‐sensitive Gln3 regulation. Accumulating evidence, however, suggests that GATA factor regulation occurs by two separate pathways, one TorC1‐dependent and the other NCR‐sensitive. Here, we identify Gln3 alterations that dissect the individual contributions of these two pathways to overall Gln3 regulation. Gln3 C‐terminal truncations or three Gln3 amino acid substitutions on one face of a putative 11 residue α‐helix completely abolish the response of Gln3 localization to Rap addition, but have no affect on its response to nitrogen limitation. This suggests that the two regulatory systems can be effectively separated. However, overall wild type control of intracellular Gln3 localization requires the contributions of both individual regulatory systems. NIH GM‐35642.