Siebel C W, Feng L, Guthrie C, Fu X D
Department of Biochemistry and Biophysics, University of California, 513 Parnassus Avenue, San Francisco, CA 94143-0448, USA.
Proc Natl Acad Sci U S A. 1999 May 11;96(10):5440-5. doi: 10.1073/pnas.96.10.5440.
SR protein kinases (SRPKs) and their substrates, the SR family of serine/arginine-rich pre-mRNA splicing factors, appear to be key regulators of alternative splicing. Although SR proteins have been well characterized through biochemical experiments in metazoans, their functions in vivo are unclear. Because of the strict splice site consensus and near absence of alternative splicing in Saccharomyces cerevisiae, it had been thought that budding yeast would lack an SRPK and its substrates. Here, we present structural, biochemical, and cell-biological evidence that directly demonstrates an SR protein kinase, Sky1p, as well as a number of SRPK substrates in S. cerevisiae. One of these substrates is Npl3p, an SR-like protein involved in mRNA export. This finding raises the provocative possibility that Sky1p, and by extension metazoan SRPKs, regulates mRNA export or the nucleocytoplasmic shuttling of RS domain proteins. The unexpected discovery of an SR protein kinase in budding yeast provides a foundation for genetic dissection of the biological functions of SR proteins and their kinases.
SR蛋白激酶（SRPKs）及其底物——富含丝氨酸/精氨酸的前体mRNA剪接因子SR家族，似乎是可变剪接的关键调节因子。尽管通过后生动物的生化实验已对SR蛋白进行了充分表征，但其在体内的功能仍不清楚。由于酿酒酵母中存在严格的剪接位点共有序列且几乎不存在可变剪接，因此人们一直认为芽殖酵母缺乏SRPK及其底物。在此，我们提供了结构、生化和细胞生物学证据，直接证明了酿酒酵母中存在一种SR蛋白激酶Sky1p以及多种SRPK底物。其中一种底物是Npl3p，一种参与mRNA输出的类SR蛋白。这一发现引发了一种引人深思的可能性，即Sky1p以及后生动物的SRPKs可能调节mRNA输出或RS结构域蛋白的核质穿梭。在芽殖酵母中意外发现SR蛋白激酶为对SR蛋白及其激酶的生物学功能进行遗传剖析奠定了基础。
