Kar4p, a karyogamy-specific component of the yeast pheromone response pathway.
Karyogamy is the process whereby two haploid nuclei fuse to form a diploid nucleus during mating in Saccharomyces cerevisiae. Here, we describe the characterization of the KAR4 gene, previously identified in a screen for new nuclear fusion-defective mutants. During mating, kar4 mutants were defective for the microtubule-dependent movement of nuclei, a phenotype identical to that of mutations in KAR3 and CIK1. Consistent with its mutant phenotype, we found that the kar4 mutation resulted in failure to induce KAR3 and CIK1 mRNA during mating. Expression of KAR3 and CIK1 under independent regulatory control suppressed the kar4 defect, indicating that KAR4 is required primarily for the induction of KAR3 and CIK1. KAR4 was also required for meiosis, during which it may regulate KAR3; however, mitotic expression of KAR3 and CIK1 during S/G2 phase was independent of KAR4. A 30-bp region upstream of KAR3 conferred both KAR4- and STE12-dependent induction by mating pheromone. This region contained one moderate and two weak matches to the consensus pheromone response element to which the Ste12p transcriptional activator binds and five repeats of the sequence CAAA(A). Overproduction of Ste12p suppressed the kar4 defect in KAR3 induction and nuclear fusion. In contrast, Ste12p-independent expression of Kar4p did not alleviate the requirement for Ste12p during KAR3 induction. We propose that Kar4p assists Ste12p in the pheromone-dependent expression of KAR3 and CIK1. KAR4 defines a novel level of regulation for the pheromone response pathway, acting at a subset of Stel2p-inducible genes required for karyogamy.
Kurihara
L J
LJ
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Stewart
B G
BG
Gammie
A E
AE
Rose
M D
MD
D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D008540:Meiosis; D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; D008969:Molecular Sequence Data; D010675:Pheromones; D012333:RNA, Messenger / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000502:physiology*
C076025:CIK1 protein, S cerevisiae; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C063504:KAR3 protein, S cerevisiae; C100923:KAR4 protein, S cerevisiae; D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; D010675:Pheromones; D012333:RNA, Messenger; C489241:STE12 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors