NUCLEOTIDE-SEQUENCE ANALYSIS OF AN ANDEAN POTATO MOTTLE VIRUS MIDDLE COMPONENT RNA CDNA CLONE - COMPARISONS OF THE ENCODED PROTEINS WITH THOSE OF OTHER COMOVIRUSES

Andean potato mottle virus (APMV) is a comovirus whose genomic structu re consists of two plus-strand RNA molecules (M- and B-RNA). Here we r eport the nucleotide sequence analysis of an APMV M-RNA cDNA done with 3,669 nucleotide (nt) residues, exclusive of the polyadenylate at the 3' end, covering approximately 99% of the APMV M-RNA. The first initi ation codon in register translates from nt 194 to 3185 a polyprotein o f 997 amino acid (aa) residues. A second initiation codon in register, beginning at nt position 416, translates a polyprotein of 923 aa. The cleavage sites used in the processing of polyprotein were identified in the long open reading frame by N-terminal microsequencing of the la rge coat protein (LCP) and the small coat protein (SCP). These dipepti de cleavage sites are Q/M for the LCP and Q/F for the SCP. In a compar ison of the deduced APMV polyprotein aa sequence with those of four ot her comoviruses, the coding regions for the putative movement protein, LCP and SCP, were found similar in length in all five species. Multip le alignment of the M-RNA sequences for each of the three genes from t he five comoviruses revealed different degrees of homology. APMV was a lways the least homologous of the five comoviruses, showing significan t aa substitutions in positions where the other comoviruses have ident ical residue or conservative substitutions.