The CLN3/SWI6/CLN2 pathway and SNF1 act sequentially to regulate meiotic initiation in Saccharomyces cerevisiae.
BACKGROUND
IME1, which is required for the initiation of meiosis, is regulated by Cln3:Cdc28 kinase, which activates the G1-to-S transition, and Snf1 kinase, which mediates glucose repression. Here we examine the pathway by which Cln3:Cdc28p represses IME1 and the relationship between Cln3:Cdc28p and Snf1p in this regulation.


RESULTS
When wild-type yeast cease growth, they express IME1 to moderate levels, intermediate between the low levels expressed during growth and the high levels expressed during sporulation. Moderate IME1 expression occurred in cln3Delta, cln1Delta cln2Delta, cdc28-4 and swi6Delta mutants, even during growth. These mutants also induced IME1 expression more rapidly than the wild-type. CLN3 required SWI6 and CLN2 to repress IME1 and IME2, but CLN1 was much less active than CLN2 in this repression. The phenotype of the cln3Delta snf1Delta double mutant indicated that Cln3:Cdc28p regulates IME1 independently of SNF1.


CONCLUSIONS
Entry into meiosis involves two independent but sequential controls, which regulate IME1 via a three position switch: (i) during growth IME1 is repressed by the CLN3/SWI6/CLN2 pathway, (ii) once growth ceases, this repression is released and IME1 is expressed at moderate levels, and (iii) subsequently, nutritional conditions that activate Snf1p allow high IME1 expression.
Purnapatre
Kedar
K
Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110-2499, USA.
Piccirillo
Sarah
S
Schneider
Brandt L
BL
Honigberg
Saul M
SM
D017489:CDC28 Protein Kinase, S cerevisiae / Q000378:metabolism; D016213:Cyclins / Q000502:physiology*; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008540:Meiosis / Q000502:physiology*; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*; D015398:Signal Transduction; D013172:Spores, Fungal; D014157:Transcription Factors / Q000502:physiology*
C082721:CLN2 protein, S cerevisiae; C079895:CLN3 protein, S cerevisiae; D016213:Cyclins; D005656:Fungal Proteins; C080326:IME1 protein, S cerevisiae; D009687:Nuclear Proteins; C075111:SWI6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; D017489:CDC28 Protein Kinase, S cerevisiae