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Gene Review

KAR4  -  Kar4p

Saccharomyces cerevisiae S288c

Synonyms: Karyogamy protein KAR4, YCL055W, YCL432, YCL55W
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High impact information on KAR4

  • Chromatin immunoprecipitation and gel shift assays confirmed that Kar4 binds to regulatory DNA sequences upstream of KAR3 [1].
  • Previously known to be required only for the transcriptional induction of KAR3 and CIK1, microarray experiments identified many genes regulated by Kar4 in both mating and mitosis [1].
  • Furthermore, the induction of Kar4 by pheromone is necessary for the delayed temporal induction of KAR3 and PRM2, genes required for efficient nuclear fusion during mating [1].
  • Several gene clusters are positively or negatively regulated by mating pheromone in a Kar4-dependent manner [1].
  • Yeast Kar4 is a putative transcription factor required for karyogamy (the fusion of haploid nuclei during mating) and possibly other functions [1].

Biological context of KAR4

  • During mating, kar4 mutants were defective for the microtubule-dependent movement of nuclei, a phenotype identical to that of mutations in KAR3 and CIK1 [2].
  • A Saccharomyces servazzii clone homologous to Saccharomyces cerevisiae chromosome III spanning KAR4, ARS 304 and SPB1 lacks the recombination enhancer but contains an unknown ORF [3].
  • Kar4p is a transcription factor in Saccharomyces cerevisiae that is required for the expression of karyogamy-specific genes during mating, for the efficient transit from G1 during mitosis, and for essential functions during meiosis [4].
  • Thus, the elaborate regulation of the two forms of Kar4p at the levels of transcription, translation, and protein turnover reflects the requirement for high levels of the protein during mating and for low levels during the subsequent phases of the cell cycle [4].
  • Analysis of the upstream regions of Kar4-induced genes identified a DNA sequence motif that may be a binding site for Kar4 [1].

Regulatory relationships of KAR4

  • Overproduction of Ste12p suppressed the kar4 defect in KAR3 induction and nuclear fusion [2].
  • However, the two forms of Kar4p could also be expressed separately from the regulatable GAL1 promoter, and no functional difference was detected when they were expressed at equivalent levels [4].

Other interactions of KAR4

  • A 30-bp region upstream of KAR3 conferred both KAR4- and STE12-dependent induction by mating pheromone [2].
  • However, there is an additional ORF in S. servazzii between PRD1 and KAR4 that is not homologous to any gene in S. cerevisiae or to genes in other organisms [3].


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