Pestivirus gene expression: the first protein product of the bovine viral diarrhea virus large open reading frame, p20, possesses proteolytic activity.

The positive-strand RNA genome of pestiviruses contains a single large open reading frame (ORF) extending its entire length and is capable of encoding 450 kDa of protein. Studies have been undertaken with the purpose of elucidating the specific mechanisms involved in the biogenesis of the complete complement of pestivirus proteins. Here, we report on gene expression at the 5' end of the genome of the prototype pestivirus, bovine viral diarrhea virus (BVDV). We demonstrate, using both a cell-free transcription-translation system and a mammalian-cell transient-expression system, that the first protein product of the large ORF of BVDV, the p20 protein, possesses a specific proteolytic activity. The p20 proteinase activity acts to release the p20 protein from the nascent polyprotein. The p20 proteinase activity is not, however, required for downstream glycoprotein processing, indicating translocation of the pestivirus glycoprotein precursor is affected by an internal signal sequence.