Structure and transcriptional status of bovine syncytial virus in cytopathic infections

The genomic structure of bovine syncytial virus (BSV), a virus commonly infecting cattle, was examined in order to gain insights into the nature of viral DNA (vDNA) intermediates and the transcriptional status of the virus in cytopathic infections. In dog Cf2Th cells, the DNA intermediate of BSV was found to exist predominantly as linear unintegrated vDNA (uvD) molecules. The uvD molecules were cloned directly from total cellular DNA by addition of EcoRI linkers and subsequent ligation into the phage lambda EMBL4 vector. Of the eleven clones characterized, seven were full length as judged by restriction fragment analysis. The remaining four clones showed varying degrees of heterogeneity in the form of internal deletions or terminal truncations. Heat denaturation and S1 nuclease analyses were used to show that vDNA isolated from Cf2Th cells contains a single-stranded (ss) gap structure located in the central region of the genome. In addition, a double-stranded (ds) 1.3-kb fragment is observed in this vDNA population. Northern-blot analysis revealed the presence of virus-specific transcripts of 11.0, 6.4, 2.8, and 2.4 kb. This suggests that BSV is similar in complexity to the lentiviruses in terms of linear intermediates containing ss gap structures, and the presence of several RNA transcripts which may direct complex regulatory functions.