Ribosomal protein genes in the yeast Candida albicans may be activated by a heterodimeric transcription factor related to Ino2 and Ino4 from S. cerevisiae.
In the yeast Saccharomyces cerevisiae, structural genes of phospholipid biosynthesis are activated by a heterodimer of basic helix-loop-helix proteins, Ino2 and Ino4, which bind to the inositol/choline-responsive element (ICRE) UAS element. In silico, we identified Candida albicans genes, which encode proteins similar to Ino2 and Ino4 (designated CaIno2 and CaIno4). CaINO4 contains an intron with an unusual branch point sequence. Although neither CaINO2 nor CaINO4 could individually complement S. cerevisiae mutations ino2 and ino4, respectively, coexpression of both CaINO2 and CaINO4 restored inositol auxotrophy of an ino2 ino4 double mutant. CaIno2 and CaIno4 could interact in vivo as well as in vitro and together were able to bind to the ICRE from S. cerevisiae INO1. Similar to Ino2 of S. cerevisiae, CaIno2 contains two transcriptional activation domains. CaIno2 and CaIno4 interact with CaSua7 (basal transcription factor TFIIB) but not with Sua7 from S. cerevisiae. Surprisingly, CaIno2 + CaIno4 were unable to stimulate expression of a CaINO1-lacZ reporter gene while an INO1-lacZ fusion was efficiently activated. This result agrees with the finding that promoter scanning of the CaINO1 upstream region gave no evidence for CaIno2 + CaIno4 binding in vitro. We derived a consensus binding site for CaIno2 + CaIno4 (BWTCASRTG), which could be detected upstream of 25 ribosomal protein genes. Since we failed to obtain homozygous deletion mutations for CaINO2 and CaINO4, we conclude that CaIno2 and CaIno4 acquired new essential target genes among which may be ribosomal protein genes.
Hoppen
Jens
J
Institut für Genetik und Funktionelle Genomforschung, Ernst-Moritz-Arndt Universität Greifswald, Jahnstr. 15a, 17487 Greifswald, Germany.
Dietz
Martin
M
Warsow
Gregor
G
Rohde
Raimund
R
Schüller
Hans-Joachim
HJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites / Q000235:genetics; D002176:Candida albicans / Q000235:genetics* / Q000378:metabolism*; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D008957:Models, Genetic; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D035581:Transcription Factor TFIIB / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D051792:Basic Helix-Loop-Helix Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; D012097:Repressor Proteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D035581:Transcription Factor TFIIB; D014157:Transcription Factors; C095723:INO2 protein, S cerevisiae; C063311:INO4 protein, S cerevisiae; C073680:SUA7 protein, S cerevisiae