%0 Journal Article
%T mRNA 3¡ä End Processing Factors: A Phylogenetic Comparison
%A Sarah K. Darmon
%A Carol S. Lutz
%J International Journal of Genomics
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/876893
%X Almost all eukaryotic mRNAs possess 3¡ä ends with a polyadenylate (poly(A)) tail. This poly(A) tail is not encoded in the genome but is added by the process of polyadenylation. Polyadenylation is a two-step process, and this process is accomplished by multisubunit protein factors. Here, we comprehensively compare the protein machinery responsible for polyadenylation of mRNAs across many evolutionary divergent species, and we have found these protein factors to be remarkably conserved in nature. These data suggest that polyadenylation of mRNAs is an ancient process. 1. Introduction Almost all eukaryotic mRNAs have a poly(A) tail at their 3¡ä ends, with the most notable exception being histone mRNAs. The process by which mRNAs acquire a poly(A) tail is termed polyadenylation. Polyadenylation is a tightly coupled, two-step process that first endonucleolytically cleaves the pre-mRNA and subsequently adds an unencoded poly(A) tail (reviewed in [1¨C7]). Poly(A) tails serve the mRNA in many ways, aiding in mRNA translation, facilitating transport from the nucleus to the cytoplasm, and promoting stability [8¨C12]. The addition of the poly(A) tail is a highly coordinated event, requiring cooperation from both cis-acting RNA sequence elements and trans-acting protein factors to complete the process [13, 14]. Alternative or regulated polyadenylation likely requires further cooperation and integration of efforts. Two sequence elements in mammals serve as the core polyadenylation elements: the AAUAAA or a variant, and a U/GU-rich element located downstream 10¨C30£¿nts of the actual site of polyadenylation (Figure 1, [15, 16] and references therein). The cleavage site, where the poly(A) tail is added, is located in between these two sequence elements and is often a CA dinucleotide, but it has some variability ([15] and references therein). The AAUAAA element serves as a binding site for the CPSF (cleavage and polyadenylation specificity factor) complex, a complex of four subunits, while the U/GU-rich element binds the CstF (cleavage stimulation factor) complex, a trimeric complex of proteins (Figure 1). Yeast polyadenylation signals have a slightly different composition but bind similar protein complexes with slightly different orientation. Figure 1: Human polyadenylation factors. Human basal polyadenylation factors are composed of many multisubunit complexes: CPSF, CstF, CFIm, and CFIIm. There are also many other auxiliary factors that contribute to polyadenylation; representative factors are listed at the top right. The protein factors that make up the basal
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