A complex containing the CCR4 and CAF1 proteins is involved in mRNA deadenylation in Drosophila

The CCR4 - NOT complex is the major enzyme catalyzing mRNA deadenylation in Saccharomyces cerevisiae. We have identified homologs for almost all subunits of this complex in the Drosophila genome. Biochemical fractionation showed that the two likely catalytic subunits, CCR4 and CAF1, were associated with each other and with a poly( A)- specific 30 exonuclease activity. In Drosophila, the CCR4 and CAF1 proteins were ubiquitously expressed and present in cytoplasmic foci. Individual knock-down of several potential subunits of the Drosophila CCR4 - NOT complex by RNAi in tissue culture cells led to a lengthening of bulk mRNA poly(A) tails. Knock-down of two individual subunits also interfered with the rapid deadenylation of Hsp70 mRNA during recovery from heat shock. Similarly, ccr4 mutant flies had elongated bulk poly( A) and a defect in Hsp70 mRNA deadenylation. A minor increase in bulk poly( A) tail length was also observed in Rga mutant flies, which are affected in the NOT2 subunit. The data show that the CCR4 - NOT complex is conserved in Drosophila melanogaster and plays a role in general and regulated mRNA deadenylation.