Three of the eight RNA segments encoded by the influenza A virus (IAV) undergo alternative splicing to generate distinct proteins. Previously, we found that host proteins hnRNP K and NS1-BP regulate IAV M segment splicing, but the mechanistic details were unknown. Here we show NS1-BP and hnRNP K bind M mRNA downstream of the M2 5' splice site (5'ss). NS1-BP binds most proximal to the 5'ss, partially overlapping the U1 snRNP binding site, while hnRNP K binds further downstream and promotes U1 snRNP recruitment. Mutation of either or both the hnRNP K and NS1-BP-binding sites results in M segment mis-splicing and attenuated IAV replication. Additionally, we show that hnRNP K and NS1-BP regulate host splicing events and that viral infection causes mis-splicing of some of these transcripts. Therefore, our proposed mechanism of hnRNP K/NS1-BP mediated IAV M splicing provides potential targets of antiviral intervention and reveals novel host functions for these proteins.

中文翻译：

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hnRNP K和NS1-BP在流感和人类mRNA剪接中的共调节活性。

由甲型流感病毒（IAV）编码的八个RNA片段中的三个经历了选择性剪接，以生成独特的蛋白质。以前，我们发现宿主蛋白hnRNP K和NS1-BP调节IAV M片段的剪接，但机制细节尚不清楚。在这里，我们显示NS1-BP和hnRNP K在M2 5'剪接位点（5's）的下游结合M mRNA。NS1-BP结合最接近5's，部分重叠U1 snRNP结合位点，而hnRNP K结合更下游，并促进U1 snRNP募集。hnRNP K和NS1-BP结合位点中的一个或两个都突变会导致M段错剪和IAV复制减弱。此外，我们显示hnRNP K和NS1-BP调节宿主剪接事件，并且病毒感染会导致其中某些转录物错接。所以，