Mechanisms for signal transduction in the initiation of meiosis in enkaryotes

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1. We isolated IME2, SME2, and SME3 genes as positive regulators for the initiation of meiosis. IME2 was transcribed specifically at an early stage of meiosis. Transcripts from SME2 and SME3 were accumulated in stationary cells. SME2 activated transcription of SGA1, a late meiosis-specific gene, independently of IME1 and IME2. SME3 activated IME1 transcription. GAM1 and GAM3, positive regulators for STA1, were also required for transcription of IME1. SUD1, GAM2, NIM1, and NIM2 were required for repression of IME2. From these results, we proposed a model for regulatory cascades governing the initiation of meiosis. 2. Using IME2-specific antisera, we demonstrated nuclear localization and protein kinase activity of IME2 protein. Carboxy-terminal domain of IME2 consisting of six highly acidic subpeptides appeared to have a negative role. 3. We also examined the mechanism for transcriptional regulation of SGA1 by IME2 kinase. 5' upstream region of SGA1 contained positive (UAS) and negative (NRE) elements for transcription. UAS activity was not regulated by IME2. Deletion of NRE activated transcription of SGA1 independently of IME2. These results suggest that IME2 kinase relieves negative regulation through NRE. We also identified UAS- and NRE-binding proteins by gel shift assay.