Abstract
The yeast CIT1 (mitochondrial citrate synthase) gene is subject to glucose repression and is further repressed by glucose plus glutamate. Based on deletion analysis of a CIT1-lacZ gene fusion, DNA sequences between -548 and -273 are required for full expression of CIT1. The region of transcription initiation and the putative TATA element are located at -150 to -100 and -195 respectively. A restriction fragment containing DNA sequences between -457 and -211 conferred activation and glucose-glutamate regulation when placed in either orientation upstream of a UAS-less heterologous yeast gene. Deletion of DNA sequences between -291 and -273 specifically eliminated derepression of CIT1, and destroyed one of two closely-spaced, potential binding sites for the HAP2,3,4 transcriptional activator protein. Ten-base-pair block substitutions in the region -367 to -348 reduced glucose-repressed expression. Thus, it appears that distinct DNA sequences upstream of CIT1 activate expression in glucose-repressed and derepressed cells. Possible mechanisms of regulation by glutamate plus glucose, are discussed.
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