POSITIVE AND NEGATIVE FEEDBACK LOOPS AFFECT THE TRANSCRIPTION OF IME1, A POSITIVE REGULATOR OF MEIOSIS IN SACCHAROMYCES-CEREVISIAE

The IME1 gene of Saccharomyces cerevisiae encodes a transcription fact or that is required for the expression of meiosis-specific genes. Like many of the genes it regulates, IME1 itself is expressed according to the following complex pattern: barely detectable levels during vegeta tive growth, and high induced levels under starvation conditions, foll owed by a subsequent decline in the course of meiosis. This report exa mines the influence of Ime1 protein on its own expression, demonstrati ng feedback regulation. Disruption of either IME1 or IME2 leads to con stantly increasing levels of Ime1-lacZ expression, under meiotic condi tions. This apparent negative regulation is due to cis elements in the IME1 upstream region, which confer transient meiotic expression to he terologous promoter-less genes. A specific DNA/protein complex, whose level is transiently increased under meiotic conditions, is detected o n this element. In ime1(-) diploids, the level of this DNA/protein com plex increases, without any decline. These results indicate that the t ransient expression of IME1 is apparently due to transcriptional regul ation. This report also presents evidence suggesting that Ime1p is dir ectly responsible for regulating its own transcription. Positive feedb ack regulation in mitotic conditions is suggested by the observation t hat overexpression of Ime1p leads to increased levels of IME1-lacZ. Ne gative autoregulation in meiotic cultures is demonstrated by the obser vation that a specific point mutation in IME1, ime1-3, permits express ion of meiosis-specific genes, as well as induction of meiosis, but is defective in negative-feedback regulation of IME1. (C) 1995 Wiley-Lis s, Inc.