Role of a Candida albicans Nrm1/Whi5 homologue in cell cycle gene expression and DNA replication stress response

Abstract

Summary To explore cell cycle regulation in the dimorphic fungus Candida albicans, we identified and characterized CaNrm1, a C. albicans homologue of the Saccharomyces cerevisiae Whi5 and Nrm1 transcription inhibitors that, analogous to mammalian Rb, regulate the cell cycle transcription programme during the G1 phase. CaNRM1 is able to complement the phenotypes of both whi5 and nrm1 mutants in S. cerevisiae. In C. albicans, global transcription analysis of the CaNRM1 deletion mutant reveals a preferential induction of G1‐ and G1/S‐specific genes. CaNrm1 interacts genetically with the C. albicans MBF functional homologue, and physically with its subunit CaSwi4. Similar to S. cerevisiae Whi5, CaNrm1 subcellular localization oscillates with the cell cycle between the nucleus and the cytoplasm. Deletion of CaNRM1 further results in increased resistance to hydroxyurea, an inhibitor of DNA replication; analysis of the expression of ribonucleotide reductase, the target of hydroxyurea, suggests that its transcriptional induction in response to hydroxyurea is regulated via CaNrm1, and biochemical analysis shows that hydroxyurea causes disruption of the interaction of CaNrm1 with CaSwi4. Furthermore, induction of the hyphal‐specific genes is dampened under certain conditions in the Canrm1−/− mutant, suggesting that the cell cycle transcription programme can influence the morphogenetic transcription programme of C. albicans.

Repression of G1/S Transcription Is Mediated via Interaction of the GTB Motifs of Nrm1 and Whi5 with Swi6

“…5A and 6A) with homologs in some very distantly related genera, including members of the Basidiomycetes (data not shown). In fact, an ortholog of Nrm1/Whi5 that contains a GTB motif was recently identified in Candida albicans (20). Together, these observations suggest that the GTB motif is a functional module that, at least based upon the behavior of Whi5 and Nrm1, is necessary and sufficient for binding to the G 1 /S transcription factor complexes.…”

“…That motif defines a protein family in S. cerevisiae that includes Whi5, Nrm1, and Srl3, a CDK-binding protein of unknown function (19). Interestingly, a protein that appears to behave as a functional homolog of both Nrm1 and Whi5 was recently identified in Candida albicans based upon the presence of that motif, which appears to be extensively conserved among fungal species (20). The motif has also been identified via bioinformatics approaches and has been named the "Whi5-like" motif (21).…”

Deciphering the Transcriptional-Regulatory Network of Flocculation in Schizosaccharomyces pombe

“…However, disruption of YOX1 in the Sacc. cerevisiae ∑1278b strain inhibited filamentous invasive growth, a process usually associated with flocculation during nutritional limitation, while deletion of C. albicans NRM1 reduced flocculation [48], [49].…”

Dot6 is a major regulator of cell size and a transcriptional activator of ribosome biogenesis in the opportunistic yeast Candida albicans

“…The transcriptional programs characterizing the cell cycle G1/S transition in C. albicans (C ote et al 2009) were hyperactivated in dot6 mutant, which is a further support of the role of Dot6 as a negative regulator of G1/S transcription and Start ( Figure 3A ). Interestingly, dot6 upregulated transcripts showed a significant correlation with those activated in the deletion mutant of the negative regulator of Start in C. albicans , Nrm1 (O fir et al 2012; S ellam et al 2016).…”