Kanopka A, Mühlemann O, Petersen-Mahrt S, Estmer C, Ohrmalm C, Akusjärvi G
Department of Medical Biochemistry and Microbiology, BMC, Uppsala University, Sweden.
Nature. 1998 May 14;393(6681):185-7. doi: 10.1038/30277.
SR proteins are a family of essential splicing factors required for early recognition of splice sites during spliceosome assembly. They also function as alternative RNA splicing factors when overexpressed in vivo or added in excess to extracts in vitro. SR proteins are highly phosphorylated in vivo, a modification that is required for their function in spliceosome assembly and splicing catalysis. Here we show that SR proteins purified from late adenovirus-infected cells are inactivated as splicing enhancer or splicing repressor proteins by virus-induced dephosphorylation. We further show that the virus-encoded protein E4-ORF4 activates dephosphorylation by protein phosphatase 2A of HeLa SR proteins and converts their splicing properties into that of SR proteins purified from late adenovirus-infected cells. Taken together, our results suggest that E4-ORF4 is an important factor controlling the temporal shift in adenovirus alternative RNA splicing. We conclude that alternative pre-mRNA splicing, like many other biological processes, is regulated by reversible protein phosphorylation.
SR蛋白是剪接体组装过程中早期识别剪接位点所需的一类重要剪接因子。当在体内过表达或在体外提取物中过量添加时，它们还可作为可变RNA剪接因子发挥作用。SR蛋白在体内高度磷酸化，这种修饰是它们在剪接体组装和剪接催化中发挥功能所必需的。在这里，我们表明，从晚期腺病毒感染细胞中纯化的SR蛋白会因病毒诱导的去磷酸化而失活，无法作为剪接增强子或剪接抑制蛋白发挥作用。我们进一步表明，病毒编码的蛋白E4-ORF4可通过HeLa细胞SR蛋白的蛋白磷酸酶2A激活去磷酸化，并将它们的剪接特性转变为从晚期腺病毒感染细胞中纯化的SR蛋白的剪接特性。综上所述，我们的结果表明E4-ORF4是控制腺病毒可变RNA剪接时间转变的一个重要因子。我们得出结论，可变前体mRNA剪接与许多其他生物学过程一样，受可逆性蛋白质磷酸化的调控。
