The deadenylase components Not2p, Not3p, and Not5p promote mRNA decapping

Decay of mRNA is essential for the efficient regulation of gene expression. A major pathway of mRNA degradation is initiated by the shortening of the poly(A) tail via the CCR4/NOT deadenylase complex. Deadenylation is followed by removal of the 5′ cap (i.e., decapping) and then 5′ to 3′ exonucleolytic decay of the message body. The highly conserved CCR4/NOT deadenylase complex consists of the exonucleases CCR4 and POP2/CAF1, as well as a group of four or five (depending on organism) accessory factors of unknown function, i.e., the NOT proteins. In this study, we find that Saccharomyces cerevisiae Not2p, Not3p, and Not5p (close paralogs of each other) are involved in promoting mRNA decapping. Furthermore, we find that Not3p and Not5p bind to the decapping activator protein Pat1p. Together, these data implicate the deadenylase complex in coordinating the downstream decapping reaction via Not2p, Not3p, and Not5p. This suggests that the coupling of deadenylation with decapping is, in part, a direct consequence of coordinated assembly of decay factors.