The P Genes of Human Parainfluenza Virus Type 1 Clinical Isolates Are Polycistronic and Microheterogeneous

The nucleotide sequence of the P gene of human parainfluenza virus type 1 (hPIV1) strain C35 was determined directly from genomic viral RNA and by molecular cloning. The gene contained 1893 nucleotides. Four open reading frames (ORF) capable of encoding a P protein (568 amino acids; M(r) = 64,784), a C' protein (219 amino acids; M(r) = 25,997), a C protein (204 amino acids; M(r) = 24,237), and a Y1 protein (182 amino acids; M(r) = 21,471) were identified. The latter three ORFs are in a +1 reading frame relative to P. The sequencing data are consistent with the hPIV1 C' protein being initiated at a GUG codon (nt 68-70), in contrast to the ACG initiation of the Sendai virus (SV) C' protein. Unlike SV, there is no evidence of a hPIV1 ORF capable of encoding a cysteine-rich V protein. Also, there is no ORF capable of encoding a protein analogous to the SV Y2 protein. In vitro transcription, translation, and immunoprecipitation showed that the hPIV1 P gene is polycistronic. Comparison of the P gene with those of two other distinct clinical isolates confirmed the coding potential of the hPIV1 P gene but also revealed genetic heterogeneity among the isolates. Our results indicate that the hPIV1 P gene uses some coding strategies similar to and others that are different from those of other paramyxovirus P genes.