Abstract
Suppression of the effects of an spt10 mutation on ADH2 expression is a phenotype shared by a small number of genes whose protein products are either components of the CCR4-NOT complex required for mRNA deadenylation and degradation (CCR4, CAF1, NOT4) or have been shown to interact with the complex (DBF2, SRB9, SRB10). In this work, we conducted a screen for additional suppressors of spt10 at ADH2 to identify new factors related to CCR4 function. In addition to reisolating ccr4 and caf1 alleles, three previously unidentified suppressors of spt10 were obtained: ebs1, lsm6, and nup159. These three genes are known or presumed to affect mRNA export or degradation. Mutations in EBS1, LSM6 and NUP159 not only suppressed spt10-induced ADH2 expression but also, like ccr4 and caf1 defects, reduced the ability of ADH2 to derepress. None of these defects affected the expression of CCR4-NOT complex components or the formation of the CCR4-NOT complex. The reduced ADH2 expression was also not the result of increased degradation of ADH2 mRNA, as the lsm6 and nup159 alleles, like that of a ccr4 deletion, actually slowed ADH2 degradation. Our results indicate that alterations in factors that slow mRNA degradation or affect mRNA transport may also interfere with the synthesis of mRNA and suggest an integration of such events in gene expression.
Highlights
The CCR4 protein is involved in several processes controlling the metabolism of mRNA in the cell: mRNA initiation, elongation, and degradation
In order to identify other factors that are functionally related to the CCR4-NOT proteins, we conducted a search for additional suppressors of the spt10 effects at the ADH2 locus using a strain carrying the defective adh1-1 allele
CCR4 has been considered an activator of transcription since it first was identified as a suppressor of spt10 effects at ADH2 and as being required for ADH2 derepression following non-fermentative growth [1,3]
Summary
The CCR4 protein is involved in several processes controlling the metabolism of mRNA in the cell: mRNA. The ability to suppress spt10-enchanced ADH2 expression reflects a common factor related to CCR4 function, and possibly to a role not directly involving effects on mRNA degradation. Utilizing this screen for suppressors of spt, we have identified three new genes which when mutated are capable of suppressing spt: NUP159, LSM6 and EBS1. These three factors, like CCR4, CAF1 and NOT4 are known or presumed to be involved in controlling mRNA export or degradation. The CCR4 requirement at ADH2 may, result from indirect effects involving the integration of mRNA synthesis with the subsequent nuclear export and degradation of mRNA
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