Abstract
The RNA binding protein Unr, which contains five cold shock domains, has several specific roles in post-transcriptional control of gene expression. It can act as an activator or inhibitor of translation initiation, promote mRNA turnover, or stabilise mRNA. Its role depends on the mRNA and other proteins to which it binds, which includes cytoplasmic poly(A) binding protein 1 (PABP1). Since PABP1 binds to all polyadenylated mRNAs, and is involved in translation initiation by interaction with eukaryotic translation initiation factor 4G (eIF4G), we investigated whether Unr has a general role in translational control. We found that Unr strongly stimulates translation in vitro, and mutation of cold shock domains 2 or 4 inhibited its translation activity. The ability of Unr and its mutants to stimulate translation correlated with its ability to bind RNA, and to interact with PABP1. We found that Unr stimulated the binding of PABP1 to mRNA, and that Unr was required for the stable interaction of PABP1 and eIF4G in cells. siRNA-mediated knockdown of Unr reduced the overall level of cellular translation in cells, as well as that of cap-dependent and IRES-dependent reporters. These data describe a novel role for Unr in regulating cellular gene expression.
Highlights
IntroductionUnr ( known as CSDE1) is a cellular RNA-binding protein with five cold shock domains, and a preference for binding purine-rich RNA sequences[1]
Unr is a cellular RNA-binding protein with five cold shock domains, and a preference for binding purine-rich RNA sequences[1]
The same pattern of results was seen with all four mRNAs (Fig. 1a–d), the difference between the translation activity of wt Unr and the CSD2 mutant was significant in each case, whereas the difference between wt Unr and the CSD4 mutant was only significant on capped polyadenylated mRNA
Summary
Unr ( known as CSDE1) is a cellular RNA-binding protein with five cold shock domains, and a preference for binding purine-rich RNA sequences[1]. There are examples of Unr regulating mRNA stability: in the case of c-fos mRNA, Unr is part of a complex that promotes translationally-coupled mRNA turnover[13], whereas Unr is part of a stabilising complex on the parathyroid hormone mRNA14. In these varied roles, Unr functions in concert with other protein partners; one such protein is PABP1, with which Unr interacts on PABP1 mRNA9, c-fos RNA13, and on msl[2] mRNA12 in Drosophila. The role of Unr in regulating cellular translation and found that Unr stimulates translation in vitro and in cells, and that this correlates with its ability to interact with PABP1
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