PgmNr Y3062: Multiple MAPK cascades regulate the transcription of IME1, the master transcriptional activator of meiosis in Saccharomyces cerevisiae.

Authors:
Y. Kassir; S. Kahana-Edwin; M. Stark


Institutes
Technion Inst, Haifa, IL.


Keyword: Signal Transduction

Abstract:

Entry into meiosis in S. cerevisiae depends on the expression and activity of a master regulator, Ime1. The transcription of IME1 is regulated by all the meiotic signals through an atypical large and complex 5' region.  In this report we focus on a distinct cis-acting regulatory element UASru, whose activity is regulated by multiple signals. A glucose signal inhibits UASru activity through the cAMP/protein kinase A pathway and the transcription factors (TF), Com2 and Sko1. A nitrogen source represses UASru activity through the TF Sum1. Our results demonstrate that all the known MAPK cascades that operate in vegetative cultures directly affects UASru function: The Hog1 MAPK transmits a high osmolarity signal to UASru through the Sko1 TF; The Mpk1 MAPK transmits an elevated temperature signal through the TFs Swi4/Mpk1 and Swi4/Mlp1; Fus3 and Kss1 MAPKs transmit novel nutrient signal to UASru through the Ste12/Ste12 and Ste12/Tec1 TFs, respectively. This signal is specific to UASru and does not affect the mating and filamentation response elements that are regulated by these MAPK and TFs. Moreover, UASru does not respond to the mating and filamentation signals. Thus, the three optional developmental pathways available to yeast, namely, meiosis, filamentation and mating are regulated by the same MAPKs in a specific manner. A hypothesis aimed to explain how specificity is achieved will be discussed.