Screaton G R, Cáceres J F, Mayeda A, Bell M V, Plebanski M, Jackson D G, Bell J I, Krainer A R
Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, UK.
EMBO J. 1995 Sep 1;14(17):4336-49. doi: 10.1002/j.1460-2075.1995.tb00108.x.
SR proteins have a characteristic C-terminal Ser/Arg-rich repeat (RS domain) of variable length and constitute a family of highly conserved nuclear phosphoproteins that can function as both essential and alternative pre-mRNA splicing factors. We have cloned a cDNA encoding a novel human SR protein designated SRp30c, which has an unusually short RS domain. We also cloned cDNAs encoding the human homologues of Drosophila SRp55/B52 and rat SRp40/HRS. Recombinant proteins expressed from these cDNAs are active in constitutive splicing, as shown by their ability to complement a HeLa cell S100 extract deficient in SR proteins. Additional cDNA clones reflect extensive alternative splicing of SRp40 and SRp55 pre-mRNAs. The predicted protein isoforms lack the C-terminal RS domain and might be involved in feedback regulatory loops. The ability of human SRp30c, SRp40 and SRp55 to modulate alternative splicing in vivo was compared with that of other SR proteins using a transient contransfection assay. The overexpression of individual SR proteins in HeLa cells affected the choice of alternative 5' splice sites of adenovirus E1A and/or human beta-thalassemia reporters. The resulting splicing patterns were characteristic for each SR protein. Consistent with the postulated importance of SR proteins in alternative splicing in vivo, we demonstrate complex changes in the levels of mRNAs encoding the above SR proteins upon T cell activation, concomitant with changes in the expression of alternatively spliced isoforms of CD44 and CD45.
SR蛋白具有一个长度可变的特征性C末端富含丝氨酸/精氨酸的重复序列（RS结构域），并构成了一个高度保守的核磷蛋白家族，该家族成员可作为必需的和可变的前体mRNA剪接因子发挥作用。我们克隆了一个编码新型人类SR蛋白SRp30c的cDNA，其RS结构域异常短。我们还克隆了编码果蝇SRp55/B52和大鼠SRp40/HRS人类同源物的cDNA。从这些cDNA表达的重组蛋白在组成型剪接中具有活性，这可通过它们补充缺乏SR蛋白的HeLa细胞S100提取物的能力得以证明。另外的cDNA克隆反映了SRp40和SRp55前体mRNA广泛的可变剪接。预测的蛋白异构体缺乏C末端RS结构域，可能参与反馈调节环。使用瞬时共转染试验，将人类SRp30c、SRp40和SRp55在体内调节可变剪接的能力与其他SR蛋白进行了比较。在HeLa细胞中单独过表达SR蛋白会影响腺病毒E1A和/或人类β地中海贫血报告基因可变5'剪接位点的选择。所产生的剪接模式对每种SR蛋白而言都具有特征性。与SR蛋白在体内可变剪接中的假定重要性一致，我们证明在T细胞激活后，编码上述SR蛋白的mRNA水平发生了复杂变化，同时伴随着CD44和CD45可变剪接异构体表达的变化。
