Expression of novel genes encoded by the paramyxovirus J virus

Abstract

Characterization of the J virus or, in keeping with recent nomenclature recommendations, J paramyxovirus (JPV) genome revealed a unique genome structure, consisting of eight genes in the order 3′-N-P/V/C-M-F-SH-TM-G-L-5′. The small hydrophobic (SH) protein and the transmembrane (TM) protein genes are predicted to encode proteins 69 and 258 aa in size, respectively. The 4401 nt attachment (G) protein gene, much larger than most other paramyxovirus attachment protein genes sequenced to date, encodes a putative 709 aa attachment protein and contains distally a second open reading frame (ORF-X) 2115 nt long. Experiments undertaken in this study were intended to confirm the sequence-based gene allocation of JPV and to determine if proteins encoded by the SH gene, the novel TM gene and ORF-X are expressed. Northern blot analyses carried out on mRNA purified from JPV-infected cells indicated that the putative transcription initiation and termination sequences flanking the SH and TM genes are functional, consistent with their allocation as discrete genes, although a high level of read-through was observed across almost all transcriptional boundaries. Probes specific to the G protein coding region and ORF-X both identified an mRNA species corresponding to the predicted length of the G gene, confirming sequence-based predictions. While the SH and TM proteins were both detected in infected cells, no evidence was found for the expression of ORF-X. Preliminary studies indicate that the novel TM protein is a type II glycosylated integral membrane protein, orientated with its C terminus exposed at the cell surface.