Introduction

Recombination of viral and host cellular nucleic acids probably plays a major role in the evolution of viruses. By this means, a virus is able to exploit a large gene pool and to acquire new properties very rapidly. The presence of cellular genes or gene fragments within the genomes of retroviruses (v-oncogenes) is well established. For other viruses, the cellular origin of certain genes has been suggested. Direct evidence is, however, difficult to obtain, probably because elaborate mutational changes of the cellular sequences occurred in the viral genomes. For some non-retro viruses, however, sequences homologous to cellular genes have been identified. We will discuss examples of these very recent recombination events with emphasis on bovine viral diarrhoea virus (BVDV).

Cellular sequences in the genome of BVDV

Identification of host cell-derived insertions

BVDV is a member of the genus pestivirus within the family Flaviviridae (Wengler, 1991). The pestiviral genome consists of single-stranded RNA with positive polarity of about 12 kilobases (kb) (Collett et aL, 1988; Meyers, Riimenapf & Thiel, 1989∧). The first third of this RNA codes for an autoprotease and four structural proteins, while the 3’ part of the genome encodes the other non-structural proteins (Collett et ai, 1991; Thiel et al., 1991). The genome of BVDV, like that of all flaviviruses, is translated into a single polyprotein which is co- and post-translationally cleaved to give rise to mature viral proteins.