The nucleoproteins of human parainfluenza virus type 1 and Sendai virus share amino acid sequences and antigenic and structural determinants.

The complete nucleotide sequence of the nucleoprotein (NP) gene of human parainfluenza virus type 1 (hPIV-1) was determined from a cDNA clone of mRNA. The mRNA is 1683 nucleotides long (excluding polyadenylic acid) and encodes a protein of 524 amino acids with a predicted Mr of 57,548. An amino acid identity of 83% was predicted between the NPs of the human pathogen hPIV-1 and the murine paramyxovirus, Sendai virus, compared to 72% similarity at the level of the nucleotide sequence. In contrast, the amino acid sequence identity between the NPs of hPIV-1 and hPIV-3 was 59%, suggesting a more distant evolutionary relationship. The NP amino acid sequences of hPIV-1 and Sendai virus were highly conserved in the amino-terminal half of the molecule, in which 395 of the first 420 amino acids were identical. Of 11 monoclonal antibodies (MAbs) targeted against the Sendai virus NP, five cross-reacted with the hPIV-1 NP. The MAbs that cross-reacted recognize epitopes within regions of high amino acid similarity between the NPs of the two viruses. Also, five of the eight MAbs raised against hPIV-1 NP cross-reacted with Sendai virus NP. Taken together, our observations suggest that the essential amino acid sequence determinants of the NP structures of hPIV-1 and Sendai virus are conserved despite changes in their nucleotide sequences during evolution. This implies that there was a selective pressure to maintain the important functional domains of the protein.