Bovine viral diarrhea virus: prevention of persistent fetal infection by a combination of two mutations affecting Erns RNase and Npro protease.

Different genetically engineered mutants of bovine viral diarrhea virus (BVDV) were analyzed for the ability to establish infection in the fetuses of pregnant heifers. The virus mutants exhibited either a deletion of the overwhelming part of the genomic region coding for the N-terminal protease N(pro), a deletion of codon 349, which abrogates the RNase activity of the structural glycoprotein E(rns), or a combination of both mutations. Two months after infection of pregnant cattle with wild-type virus or either of the single mutants, the majority of the fetuses contained virus or were aborted or found dead in the uterus.

The carboxy-terminal sequence of the pestivirus glycoprotein E(rns) represents an unusual type of membrane anchor.

The E(rns) protein is a structural glycoprotein of pestiviruses that lacks a typical membrane anchor sequence and is known to be secreted from the infected cell. However, major amounts of the protein are retained within the cell and attached to the virion by a so far unknown mechanism. Transient-expression studies with cDNA constructs showed that in a steady-state situation, 16% of the protein is found in the supernatant of the transfected cells while 84% appears as intracellular protein.