The transcription factor Pap1/Caf3 plays a central role in the determination of caffeine resistance in Schizosaccharomyces pombe.
We previously identified four nuclear genes (caf1+-caf4+) in Schizosaccharomyces pombe, mutations in which confer resistance to caffeine and brefeldin A. caf1+, caf2+ and caf4+ were sequenced and found to be identical to the multidrug-resistance/stress-response genes hba1, crm1 and trr1, respectively. Here we show that caf3 is allelic to pap1, which encodes an AP-1-like transcription factor. The allele associated with caffeine resistance, caf3-89, contains a single-nucleotide exchange that results in a Leu-->Ser exchange in the NES (nuclear export signal) domain of the gene product. Due to this alteration, the modified protein can not be exported from the nucleus back into the cytoplasm, and thus accumulates in the nucleus. The activity of pap1/caf3 is shown to be necessary for manifestation of the caffeine resistance caused by mutations in the genes hba1/caf1 and crm1/caf2. We also cloned two genes that confer caffeine resistance when carried on a multicopy plasmid. One of them turned out to be a truncated allele of pad1/bfr2/sks1, which codes for a subunit of the 26 S proteosome. The putative product of the other gene, designated caf5, has a structure highly similar to that of MFS permeases. It contains two groups of six transmembrane spanning domains each, with the conserved motifs WRW, PET and GAIGGPVLGP in the fifth and sixth domains. These results are all consistent with our earlier hypothesis, which suggested that the caf genes are functionally interlinked in a complex detoxification mechanism. caf5 and pad1 may also encode parts of this mechanism.
Benko
Z
Z
Department of Genetics, University of Debrecen, PO Box 56, H-4010 Debrecen, Hungary.
Fenyvesvolgyi
C
C
Pesti
M
M
Sipiczki
M
M
D000483:Alleles; D000595:Amino Acid Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002110:Caffeine; D004268:DNA-Binding Proteins / Q000235:genetics*; D026141:Drug Resistance, Multiple, Fungal / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics*; D006861:Hydrogen Peroxide; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics; D000073718:Pancreatitis-Associated Proteins; D010447:Peptide Hydrolases / Q000235:genetics; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D046988:Proteasome Endopeptidase Complex; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology
D050976:Basic-Leucine Zipper Transcription Factors; C484808:Caf5 protein, S pombe; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D008565:Membrane Proteins; D000073718:Pancreatitis-Associated Proteins; C105096:Pap1 protein, S pombe; C000612141:REG3A protein, human; D029702:Schizosaccharomyces pombe Proteins; D014157:Transcription Factors; D002110:Caffeine; D006861:Hydrogen Peroxide; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease