Structural basis for an essential subunit interaction in influenza virus RNA polymerase PB1-PB2

流感病毒RNA依赖的RNA聚合酶是一种多功能的异三聚体，它利用“帽子抢夺”机制来产生病毒的mRNA。宿主细胞的信使核糖核酸被切割，产生一种带帽的寡核苷酸，它可以用病毒基因组RNA作为模板来延伸。帽子结合和核酸内切酶活性只有在病毒基因组RNA结合时才被激活。这需要从RNA结合的PB1亚基到帽结合的PB2亚基的信号，而这两个亚基之间的接口对于聚合酶的活性是必不可少的。我们用蛋白质结晶学定义了这种相互作用面，并测试了突变的接触残基对全酶功能的影响。这个新的界面令人惊讶地小，但它在调节250 kDa聚合酶方面发挥着关键作用，并且在禽流感和人类流感中完全保守。

Influenza virus RNA-dependent RNA polymerase is a multi-functional heterotrimer, which uses a "cap-snatching" mechanism to produce viral mRNA. Host cell mRNA is cleaved to yield a cap-bearing oligonucleotide which can be extended using viral genomic RNA as a template. The cap binding and endonuclease activities are only activated once viral genomic RNA is bound. This requires signaling from the RNA-binding PB1 subunit to the cap-binding PB2 subunit, and the interface between these two subunits is essential for polymerase activity. We have defined this interaction surface by protein crystallography, and tested the effects of mutating contact residues on the function of the holo-enzyme. This novel interface is surprisingly small, yet it plays a crucial role in regulating the 250 kDa polymerase, and is completely conserved among avian and human influenza.