Chapon C, Legrain P
Département de Biologie Moléculaire, Institut Pasteur, Paris, France.
EMBO J. 1992 Sep;11(9):3279-88. doi: 10.1002/j.1460-2075.1992.tb05406.x.
Processing and export of nuclear pre-mRNA are believed to be competing processes in the nucleus. In order to identify factors which are involved in these processes, we isolated suppressors that relieve the growth defect of a prp9-1 temperature-sensitive mutant strain of Saccharomyces cerevisiae. The prp9-1 mutation was previously shown to abolish splicing and to target pre-mRNA to the cytoplasm. One of the suppressors, spp91-1, corrects the prp9-1 growth defect through partial restoration of splicing and by a complete reversion of the pre-mRNA escape phenotype. This suppressor is specific for two prp9 alleles and cannot substitute for PRP9 function. The mutant and wild-type alleles of SPP91 were cloned and sequenced. SPP91 encodes a novel protein essential for mitotic growth whose sequence contains motifs indicative of a nuclear localization. In vivo depletion of SPP91 in a prp9-1 genetic background is lethal and is associated with reduced amounts of spliced mRNA and accumulation of pre-mRNA. This observation strongly supports the hypothesis that SPP91 encodes a PRP factor. We suggest that spp91-1 increases pre-mRNA retention in the nucleus by improving the formation of the spliceosome and thereby allowing a larger proportion of the pre-mRNA molecules to be spliced.
核内前体mRNA的加工和输出被认为是细胞核内相互竞争的过程。为了鉴定参与这些过程的因子，我们筛选出了能够缓解酿酒酵母prp9-1温度敏感突变株生长缺陷的抑制子。之前的研究表明，prp9-1突变会导致剪接功能丧失，并使前体mRNA靶向细胞质。其中一个抑制子spp91-1，通过部分恢复剪接以及完全逆转前体mRNA逃逸表型来纠正prp9-1的生长缺陷。这个抑制子对两个prp9等位基因具有特异性，且不能替代PRP9的功能。我们克隆并测序了SPP91的突变型和野生型等位基因。SPP91编码一种对有丝分裂生长至关重要的新型蛋白质，其序列含有表明核定位的基序。在prp9-1遗传背景下对SPP91进行体内消耗是致死的，并且与剪接mRNA量的减少和前体mRNA的积累有关。这一观察结果有力地支持了SPP91编码一种PRP因子的假说。我们认为，spp91-1通过改善剪接体的形成增加了前体mRNA在细胞核内的保留，从而使更大比例的前体mRNA分子能够被剪接。
