Shih S R, Krug R M
Rutgers University, Department of Molecular Biology and Biochemistry, Piscataway, NJ 08855, USA.
EMBO J. 1996 Oct 1;15(19):5415-27.
We show that a cellular nuclear protein, the SR splicing factor SF2/ASF, controls the level of production of an essential influenza virus protein, the M2 ion channel protein. The M2 mRNA that encodes the ion channel protein is produced by alternative splicing of another viral mRNA, M1 mRNA. The production of M2 mRNA is controlled in two ways. First, a distal (stronger) 5' splice site in M1 mRNA is blocked by the complex of viral polymerase proteins synthesized during infection, allowing the cellular splicing machinery to switch to the proximal (weaker) M2 5' splice site. Second, utilization of the weak M2 5' splice site requires its activation by the cellular SF2/ASF protein. This activation is mediated by the binding of the SF2/ASF protein to a purine-rich splicing enhancer sequence that is located in the 3' exon of M1 mRNA. We demonstrate that activation of the M2 5' splice site is controlled by the SF2/ASF protein in vivo during influenza virus infection. Utilizing four cell lines that differ in their levels of production of the SF2/ASF protein, we show that during virus infection of these cell lines both M2 mRNA and the M2 ion channel protein are produced in amounts that are proportional to the different expression levels of the SF2/ASF protein.
我们发现，一种细胞核蛋白，即SR剪接因子SF2/ASF，可控制一种重要的流感病毒蛋白——M2离子通道蛋白的产生水平。编码离子通道蛋白的M2 mRNA是由另一种病毒mRNA，即M1 mRNA的可变剪接产生的。M2 mRNA的产生受两种方式控制。首先，感染期间合成的病毒聚合酶蛋白复合物会阻断M1 mRNA中一个远端（更强的）5'剪接位点，使细胞剪接机制转而使用近端（较弱的）M2 5'剪接位点。其次，弱的M2 5'剪接位点的使用需要细胞中的SF2/ASF蛋白对其进行激活。这种激活是由SF2/ASF蛋白与位于M1 mRNA 3'外显子中的富含嘌呤的剪接增强子序列结合介导的。我们证明，在流感病毒感染期间，M2 5'剪接位点的激活在体内受SF2/ASF蛋白控制。利用四种SF2/ASF蛋白产生水平不同的细胞系，我们发现，在这些细胞系感染病毒期间，M2 mRNA和M2离子通道蛋白的产生量与SF2/ASF蛋白的不同表达水平成正比。
