Characterization of a molluscum contagiosum virus homolog of the vaccinia virus p37K major envelope antigen.

We present the first nucleotide sequence data for molluscum contagiosum virus (MCV), an unclassified poxvirus. A 2,276-bp XhoI fragment from a near left-terminal fragment of MCV subtype I (MCVI) and a 1,920-bp XhoI fragment from the corresponding locus of MCV subtype II (MCVII) were sequenced and analyzed for open reading frames (ORFs). A large, complete ORF of 1,167 bp was present in both fragments. The putative polypeptide has a calculated molecular mass of 43 kDa (p43K protein) and was shown to have a high degree of homology to the vaccinia virus p37K major envelope antigen (40% amino acid identity and 22% conservative changes). The nucleotide content of the MCV fragments sequenced was 66% G or C. The codon usage within the gene for p43K reflected this high G + C content, with position 3 of codons being predominantly G or C (82 and 87% for MCVI and MCVII, respectively). The MCV p43K-encoding gene has motifs immediately upstream which are similar to those required for vaccinia virus late gene expression. The location and direction of transcription of the MCV p43K-encoding gene were equivalent to those of the vaccinia virus p37K gene, revealing similarity in genetic organization between MCV and vaccinia virus. Another, incomplete ORF was identified downstream of the p43K-encoding gene in both MCVI and MCVII. The sequence immediately upstream of this ORF overlapped the termination codon of the p43K-encoding gene and contained a motif which had homology to the derived consensus sequence for vaccinia virus early gene promoters.