RESUMEN
Nucleosome destabilization by histone variants and modifications has been implicated in the epigenetic regulation of gene expression, with the histone variant H2A.Z and acetylation of H3K56 (H3K56ac) being two examples. Here we find that deletion of SWR1, the major subunit of the SWR1 complex depositing H2A.Z into chromatin in exchange for H2A, promotes epigenetic white-opaque switching in Candida albicans. We demonstrate through nucleosome mapping that SWR1 is required for proper nucleosome positioning on the promoter of WOR1, the master regulator of switching, and that its effects differ in white and opaque cells. Furthermore, we find that H2A.Z is enriched adjacent to nucleosome-free regions at the WOR1 promoter in white cells, suggesting a role in the stabilization of a repressive chromatin state. Deletion of YNG2, a subunit of the NuA4 H4 histone acetyltransferase (HAT) that targets SWR1 activity through histone acetylation, produces a switching phenotype similar to that of swr1, and both may act downstream of the GlcNAc signaling pathway. We further uncovered a genetic interaction between swr1 and elevated H3K56ac with the discovery that the swr1 deletion mutant is highly sensitive to nicotinamide. Our results suggest that the interaction of H2A.Z and H3K56ac regulates epigenetic switching at the nucleosome level, as well as having global effects.
Asunto(s)
Candida albicans/metabolismo , Proteínas Fúngicas/metabolismo , Histonas/metabolismo , Procesamiento Proteico-Postraduccional , ARN Helicasas/metabolismo , Acetilación , Candida albicans/genética , Ensamble y Desensamble de Cromatina , Proteínas Fúngicas/genética , Eliminación de Gen , Regulación Fúngica de la Expresión Génica , Histona Acetiltransferasas/genética , Histona Acetiltransferasas/metabolismo , Histonas/genética , Nucleosomas/genética , Nucleosomas/metabolismo , ARN Helicasas/genéticaRESUMEN
The human fungal pathogen Candida albicans undergoes white-opaque phenotypic switching, which enhances its adaptation to host niches. Switching is controlled by a transcriptional regulatory network of interlocking feedback loops acting on the transcription of WOR1, the master regulator of white-opaque switching, but regulation of the network on the translational level is not yet explored. Here, we show that the long 5' untranslated region of WOR1 regulates the white-opaque phenotype. Deletion of the WOR1 5' UTR promotes white-to-opaque switching and stabilizes the opaque state. The WOR1 5' UTR reduces translational efficiency and the association of the transcript with polysomes. Reduced polysome association was observed for additional key regulators of cell fate and morphology with long 5' UTR as well. Overall, we find a novel regulatory step of white-opaque switching at the translational level. This translational regulation is implicated for many key regulators of cell fate and morphology in C. albicans.
Asunto(s)
Regiones no Traducidas 5' , Candida albicans/genética , Candida albicans/metabolismo , Proteínas Fúngicas/genética , Regulación Fúngica de la Expresión Génica , Proteínas Fúngicas/metabolismo , Genes del Tipo Sexual de los Hongos/genética , Genes de Cambio , Humanos , Fenotipo , Polirribosomas/genética , Polirribosomas/metabolismo , Factores de Transcripción/metabolismoRESUMEN
Yeast Mrc1, ortholog of metazoan Claspin, is both a central component of normal DNA replication forks and a mediator of the S phase checkpoint. We report that Mrc1 interacts with Pol2, the catalytic subunit of DNA polymerase epsilon, essential for leading-strand DNA replication and for the checkpoint. In unperturbed cells, Mrc1 interacts independently with both the N-terminal and C-terminal halves of Pol2 (Pol2N and Pol2C). Strikingly, phosphorylation of Mrc1 during the S phase checkpoint abolishes Pol2N binding, but not Pol2C interaction. Mrc1 is required to stabilize Pol2 at replication forks stalled in HU. The bimodal Mrc1/Pol2 interaction may be an additional step in regulating the S phase checkpoint response to DNA damage on the leading strand. We propose that Mrc1, which also interacts with the MCMs, may modulate coupling of polymerization and unwinding at the replication fork.