Saccharomyces cerevisiae GATA sequences function as TATA elements during nitrogen catabolite repression and when Gln3p is excluded from the nucleus by overproduction of Ure2p

Saccharomyces cerevisiae selectively uses good nitrogen sources (glutamine) in preference to poor ones (proline) by repressing GATA factor-dependent t ranscription of the genes needed to transport and catabolize poor nitrogen sources, a physiological process designated nitrogen catabolite repression (NCR), We show that some NCR-sensitive genes (CAN1, DAL5, DUR1,2, and DUR3) produce two transcripts of slightly different sizes. Synthesis of the shor ter transcript is NCR-sensitive and that of the longer transcript is not. T he longer transcript also predominates in gEn3 Delta mutants irrespective o f the nitrogen source provided. We demonstrate that the longer mRNA species arises through the use of an alternative transcription start site generate d by Gln3p-binding sites (GATAAs) being able to act as surrogate TATA eleme nts. The ability of GATAAs to serve as surrogate TATAs, i.e, when synthesis of the shorter, NCR-sensitive transcripts are inhibited, correlates with s equestration of enhanced green fluorescent protein (EGFP)-Gln3p in the cyto plasm in a way that is indistinguishable from that seen with EGFP-Ure2p, Ho wever, when the shorter, NCR-sensitive DAL5 transcript predominates, EGFP-G ln3p is nuclear. These data suggest that the mechanism underlying NCR invol ves the cytoplasmic association of Ure2p with Gln3p, an interaction that pr events Gln3p from reaching it is binding sites upstream of NCR-sensitive ge nes.