The predicted molecular weight of the JV N-term is 35.3 kDa, based on the site of initiation of translation and location of conserved cleavage sites. The appearance, therefore, of a previously unseen 42 kDa protein in the in vitro transcription and translation profile was unexpected but this protein does represent a translation product for the JV 59GS. To date, it has not been possible to explain the difference in the predicted and observed sizes for the JV N-term, and the addition of the 14 amino acid V5 epitope within JV N-term does not account for this apparent large shift in molecular weight. However, a recent study described a similar anomaly when investigating proteolytic processing in the murine norovirus MNV-1 [12] . The predicted molecular weight for the MNV-1 N-term protein was 38.3 kDa. The authors successfully generated antisera against the MNV-1 N-term and used it to immunoprecipitate the protein from in vitro transcription and translation reactions and observed that the N-term existed as a 45 kDa doublet, in addition to the predicted size of 38 kDa. However, when MNV-1 N-term antisera was used to probe MNV-1-infected cell lysates only the 43-45 kDa doublet and a large 115 kDa precursor could be detected, suggesting that the predicted 38 kDa form of the N-term is not generated in cell culture. Again, it was not possible to conclusively determine the cause of this discrepancy, but it was speculated that the N-term protein may migrate abnormally in SDS-PAGE, or may be proteolytically processed at a previously unknown cleavage site downstream of the protein's predicted C-terminus. It is also possible that the N-term protein might be modified in some way leading to a shift in observed molecular weight. At this time the same conclusions would seem appropriate for the JV N-term. In addition, it is not known why the JV N-term was previously not detected in in vitro transcription and translation studies prior to the insertion of the V5 epitope. It cannot be ruled out, however, that the wild type JV N-term aberrantly co-migrates with the 39 kDa JV 2C protein in SDS-PAGE. Indeed, the appearance of the V5/ N-term product from transfected cell lysates would appear to be one of a doublet (Figure 8) , also analogous to the observed appearance of the MNV N-term protein in infected cells, suggesting the likelihood of a further cleavage site within the JV N-term protein which has yet to be elucidated. Nevertheless, these studies clearly demonstrate that a protein representative of the 59GS of JV is translated both in vitro and in vivo and is proteolytically processed from the ORF1 polyprotein following translation initiation at nucleotide 22.