SIAH1 targets the alternative splicing factor T-STAR for degradation by the proteasome.
T-STAR is one of three members of the SAM68 family of RNA-binding proteins that have been shown to be involved in various gene expression pathways including the control of pre-mRNA splicing. We employed a two-hybrid screen to identify proteins that interact with human T-STAR. The predominant interacting proteins were the E3 ubiquitin ligases SIAH1 and SIAH2. We found that SIAH1 bound to an octapeptide sequence in T-STAR targeting it for proteasome-dependent degradation. Rodent T-STAR orthologues (also known as etoile or SLM2) were not targeted for degradation by SIAH1. However a double amino acid substitution of mouse T-STAR that mimics the human SIAH1- binding site brought mouse T-STAR under in vivo control of SIAH1. Using a minigene transfection assay for alternative splicing activity we showed that human T-STAR, like its rodent orthologues can influence splice site choice and that human, but not mouse, T-STAR-dependent alternative splicing is modulated by SIAH1. Western blots of protein from purified germ cells indicated that SIAH1 protein expression peaks in meiosis. In mouse, T-STAR is co-expressed with SIAH1 during meiosis but, in humans, T-STAR is only strongly expressed after meiosis. Comparative sequence analysis showed SIAH- mediated proteasomal degradation of T-STAR has evolved in the primate lineage. Collectively these data suggest that SIAH- mediated down regulation of alternative splicing may be an important developmental difference between otherwise highly conserved T-STAR proteins.[1]References
- SIAH1 targets the alternative splicing factor T-STAR for degradation by the proteasome. Venables, J.P., Dalgliesh, C., Paronetto, M.P., Skitt, L., Thornton, J.K., Saunders, P.T., Sette, C., Jones, K.T., Elliott, D.J. Hum. Mol. Genet. (2004) [Pubmed]
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