IME1 GENE ENCODES A TRANSCRIPTION FACTOR WHICH IS REQUIRED TO INDUCE MEIOSIS IN SACCHAROMYCES-CEREVISIAE

Previous studies have shown that the IME1 gene is required for sporula tion and the expression of meiosis specific genes in Saccharomyces cer evisiae. However, sequence analysis has not revealed the precise funct ional role of the Ime1 protein. By engineering constructs which expres s various portions of the Ime1 p fused to either the DNA binding or tr anscriptional activation domains of GAL4, we have conclusively demonst rated that IME1 is a transcription factor, apparently required for spo rulation to activate the transcription of meiosis specific genes. The full Ime1p, when fused to the GAL4 DNA binding do main, can both activ ate GAL1-lacZ expression, and complement ime 1-0 (a null allele) for t he ability to sporulate, and transcriptionally activate IME2, a meiosi s specific gene. As successively larger portions of the encoded Ime1 p N-terminus are deleted from the GAL4(bd)-IME1 construct, the encoded fusion proteins retain the ability to complement an ime 7 null allele, despite a decreasing ability to activate GAL 1-lacZ transcription. Ho wever, a fusion construct which retains only the last 45 C-terminal am ino acids of IME1 provides neither transcriptional activation of GAL1- lacZ nor complementation of ime 1-0. Fusion of a GAL4 activation domai n to this portion of IME1, results in a construct with a restored abil ity to complement an ime1-0 allele. This restored ability is dependent upon galactose induction. We conclude, therefore, that IME1 functions in meiosis as a transcriptional activator. (C) 1994 Wiley-Liss, Inc.