Strain-variable editing during transcription of the P gene of mumps virus may lead to the generation of non-structural proteins NS1 (V) and NS2.

The sequence of the P (phosphoprotein) gene of mumps virus has been determined. It has two open reading frames, the first of which probably encodes the NS1 (or V) protein of mumps virus. Expression of the P protein requires the insertion of two non-templated residues to link the two ORFs in a process analogous to that observed in the P/V gene of simian virus type 5 to which mumps virus is closely related. Strain differences in the accuracy of insertion of non-templated G residues in the P/V gene transcripts have been described.