Date of Award

Fall 2006

Project Type

Dissertation

Program or Major

Biochemistry

Degree Name

Doctor of Philosophy

First Advisor

Clyde L Denis

Abstract

The CAF1 protein is a component of the CCR4-NOT deadenylase complex. While yeast CAF1 displays deadenylase activity, this activity is not required for its function in vivo, and CCR4 is the primary deadenylase in the complex. In order to identify CAF1-specific functional regions required for deadenylation in vivo, we targeted for mutagenesis six regions of CAF1 that are specifically conserved among CAF1 orthologs. Defects in three regions of the CAF1 protein (residues 173-175, residues 255-257 and residues 340-342, alleles caf1-1, caf1-3 and caf1-6, respectively) were found to dramatically reduce the rate of deadenylation in vivo and to result in typical caf1 deletion phenotypes without critically affecting the ability of CAF1 to bind CCR4. In contrast, defects in residues 213-215, which were defined as the site required for binding CCR4 (caf1-2 allele), reduced the rate of deadenylation to a lesser extent than did caf1-1, -3 or -6 and its in vivo phenotypes were correspondingly less severe than these other alleles. The caf1-1, -3, and -6 alleles or a caf1 deletion, unlike that of ccr4 or caf1-2, were synthetically lethal with defects in DHH1, a decapping regulator that is involved in controlling translation, and with certain defects in poly(A) binding protein (PAB1) that display decreased rates of translation and deadenylation. A caf1 deletion also had a more significant effect on translation than did ccr4. These and other genetic experiments suggest a role for CAF1 in translation separate from that of CCR4. Conversely, a pab1 translation defect that did not affect deadenylation by itself or with ccr4 severely blocked deadenylation when coupled with a caf1 deletion. These results support a role for CAF1 in communications between translation and deadenylation that are required for both processes.

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