CIS-ACTING RNA ELEMENTS REQUIRED FOR REPLICATION OF BOVINE VIRAL DIARRHEA VIRUS HEPATITIS-C VIRUS 5' NONTRANSLATED REGION CHIMERAS

Pestiviruses, such as bovine viral diarrhea virus (BVDV), share many s imilarities with hepatitis C virus (HCV) yet are more amenable to viro logic and genetic analysis. For both BVDV and HCV, translation is init iated via an internal ribosome entry site (IRES). Besides IRES functio n, the viral 5' nontranslated regions (NTRs) may also contain cis-acti ng RNA elements important for viral replication. A series of chimeric RNAs were used to examine the function of the BVDV 5' NTR. Our results show that: (1)the HCV and the encephalomyocarditis virus (EMCV) IRES element can functionally replace that of BVDV; (2) two 5' terminal hai rpins in BVDV genomic RNA are important for efficient replication; (3) replacement of the entire BVDV 5' NTR with those of HCV or EMCV leads to severely impaired replication; (4) such replacement chimeras are u nstable and efficiently replicating pseudorevertants arise; (5) pseudo revertant mutations involve deletion of 5' sequences and/or acquisitio n of novel 5' sequences such that the 5' terminal 3-4 bases of BVDV ge nome RNA are restored. Besides providing new insight into functional e lements in the BVDV 5' NTR, these chimeras may prove useful as pestivi rus vaccines and for screening and evaluation of anti-HCV IRES antivir als.