Granot, D., Department of Genetics, The Hebrew University, Jerusalem, 91904, Israel
Margolskee, J.P., Department of Genetics, The Hebrew University, Jerusalem, 91904, Israel
Simchen, G., Department of Genetics, The Hebrew University, Jerusalem, 91904, Israel

Meiosis and sporulation in yeast are subject to two types of regulation. The first depends on environmental conditions. The second depends on a genetic pathway which involves the control of the positive regulatory gene IME1 by RME1, which is in turn controlled by the MAT locus. The presence of IME1 on a multicopy plasmid enables cells to undergo meiosis regardless of their genotype at MAT or RME1. We show here that a multicopy plasmid carrying IME1 also enables meiosis, regardless of the environment. Therefore, both kinds of regulation appear to act through IME1. Furthermore, the behavior of multicopy plasmids carrying various segments from the IME1 region suggests that the region upstream of IME1 contains both positive and negative regulatory sites. Control of IME1 by the environment and by the MAT pathway both act through negative regulatory sites. © 1989 Springer-Verlag.