Structure and function of the Bovine Viral Diarrhea Virus 3' UTR during the virus life cycle.

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Bovine viral diarrhea virus (BVDV) is an important pathogen to the cattle industry, through both acute and persistent infections (PI). Acute infections decrease reproduction in both male and females cattle, and PI calves are sources of infection. PI calves result from in utero BVDV infection of the fetus in acutely infected pregnant females. Control of BVDV involves identification and culling of PI calves, and vaccination. However, vaccination with modified live vaccines can lead to the birth of PI calves if vaccines are accidently given to pregnant females. ******BVDV has a + stranded RNA genome and its replication is regulated by the structure of the RNA genome and protein that bind to it. In particular, the 5' and 3' end regions, the un-translated regions (UTRs), contain sequences and structures that regulate virus translation and replication. In addition, the UTRs of a few viruses, hepatitis C virus (HCV) and BVDV, also bind miRNAs that promote the virus life-cycle, possibly by modulating the functions of the RNA to which they bind and altering RNA structures and/or protein binding at that region. ******The long-term objective of my research is to understand how the BVDV 5' and 3' UTRs regulate virus replication so that we can identify ways to develop attenuated viral vaccines or control the cellular tropism of the virus and prevent infection of the fetus. In this proposal, our short-term objectives are to analyze the role of the BVDV 3 UTR in regulating the virus' life cycle. The 3' UTR is a structured RNA element and recent research showed that host cellular microRNAs, miR-17 and let-7, anneal to the 3' UTR and promote BVDV replication. We have preliminary data showing that small RNAs other than miR-17 or let-7 that also anneal to the 3' UTR can also promote BVDV replication. This suggests that any small RNA that binds is sufficient to promote virus replication, as long as it binds to the right region of the genome. Our goal is to identify the boundary of the domain to which miRNA annealing can promote BVDV replication. We will also determine the role of this domain in the virus' life cycle by analyzing growth of viruses having point mutations to this region. Finally we will identify the role of this domain in BVDV replication by analyzing the proteins that bind to it, how annealing of the miRNAs changes protein binding, and how this regulates BVDV replication. ******These studies will lead to a better understanding of the BVDV life cycle and the roles of the 3' UTR and its binding proteins and RNAs. This work may also identify ways to make new attenuated vaccines and strategies to limit vaccine replication to specific cell times and thus avoid vaccine spread to the fetus and prevent birth of PI calves from vaccinated pregnant cows.