Molecular Characterization of Hap Complex Components Responsible for Methanol-Inducible Gene Expression in the Methylotrophic Yeast Candida boidinii

Abstract

ABSTRACT We identified genes encoding components of the Hap complex, CbHAP2 , CbHAP3 , and CbHAP5 , as transcription factors regulating methanol-inducible gene expression in the methylotrophic yeast Candida boidinii . We found that the Cbhap2 Δ, Cbhap3 Δ, and Cbhap5 Δ gene-disrupted strains showed severe growth defects on methanol but not on glucose and nonfermentable carbon sources such as ethanol and glycerol. In these disruptants, the transcriptional activities of methanol-inducible promoters were significantly decreased compared to those of the wild-type strain, indicating that CbHap2p, CbHap3p, and CbHap5p play indispensable roles in methanol-inducible gene expression. Further molecular and biochemical analyses demonstrated that CbHap2p, CbHap3p, and CbHap5p localized to the nucleus and bound to the promoter regions of methanol-inducible genes regardless of the carbon source, and heterotrimer formation was suggested to be necessary for binding to DNA. Unexpectedly, distinct from Saccharomyces cerevisiae , the Hap complex functioned in methanol-specific induction rather than glucose derepression in C. boidinii . Our results shed light on a novel function of the Hap complex in methanol-inducible gene expression in methylotrophic yeasts.