The mammalian orthoreovirus bicistronic M3 mRNA initiates translation using a 5′ end-dependent, scanning mechanism that does not require interaction of 5′-3′ untranslated regions

Mammalian orthoreovirus mRNAs possess short 5 ' UTR, lack 3 ' poly(A) tails, and may lack 5 ' cap structures at late times post-infection. As such, the mechanisms by which these viral mRNAs recruit ribosomes remain completely unknown. Toward addressing this question, we used bicistronic MRV M3 mRNA to analyze the role of 5 ' and 3 ' UTRs during MRV protein synthesis. The 5 ' UTR was found to be dispensable for translation initiation; however, reducing its length promoted increased downstream initiation. Modifying start site Kozak context altered the ratio of upstream to downstream initiation, whereas mutations in the 3 ' UTR did not. Moreover, an M3 mRNA lacking a 3 ' UTR was able to rescue MRV infection to WT levels in an siRNA trans-complementation assay. Together, these data allow us to propose a model in which the MRV M3 mRNA initiates translation using a 5 ' end-dependent, scanning mechanism that does not require the viral mRNA 3 ' UTR or 5 '-3 ' UTRs interaction. (c) 2014 Elsevier B.V. All rights reserved.