Molecular Cloning and Sequence Analysis of the Mumps Virus Gene Encoding the P Protein: Mumps Virus P Gene Is Monocistronic

This study determined the nucleotide sequence of the mumps virus P (phosphoprotein) gene from two viral strains using overlapping cDNA clones. The P gene contains a single open reading frame encoding 391 amino acids with a calculated molecular weight of 41,587 Da, consistent with electrophoretic estimates of 40-45 kDa. Notably, the mumps virus P gene is monocistronic, lacking a second open reading frame analogous to the C gene found in other paramyxoviruses like Sendai virus, parainfluenza virus 3, and measles virus. The nucleotide sequences of the attenuated Miyahara vaccine strain and the Enders strain showed 95% homology, with 4% amino acid variation. Hybrid-arrested translation experiments identified a 25 kDa truncated protein product, suggesting synthesis of shorter P protein variants in infected cells. Limited amino acid sequence homology was detected between mumps virus P protein and Newcastle disease virus P protein, but none with Sendai virus. The findings suggest mumps virus utilizes truncated P proteins rather than separately encoded C proteins for non-structural functions, distinguishing it from some other paramyxoviruses that employ overlapping reading frames.

Key findings

• The mumps virus P gene is monocistronic, containing a single 1,173-nucleotide open reading frame encoding a 391-amino-acid phosphoprotein with Mr of 41,587 Da
• No second open reading frame analogous to paramyxovirus C genes exists in the mumps P gene region, distinguishing it from Sendai, parainfluenza 3, and measles viruses
• Two mumps virus strains (Miyahara and Enders) show 95% nucleotide and 96% amino acid sequence identity, with limited homology to Newcastle disease virus P protein but none to Sendai virus
• Evidence of truncated P protein variants (25 kDa product) suggests alternative translation initiation from internal ATG codons in mumps-infected cells