Nucleic Acids Research

The complete nucleotide sequence of the maize chlorotic mottle virus (MCMV) genome has been determined to be 4437 nucleotides. The viral genome has four long open reading frames (ORFs) which could encode polypeptides of 31.6, 50, 8.9 and 25.1 kd. If the termination codons for the polypeptides encoded by the 50 and 8.9 kd ORFs are suppressed, readthrough products of 111 and 32.7 kd result. The 31.6 and 50 kd ORFs overlap for nearly the entire length of the 31.6 kd ORF. Striking amino acid homology has been observed between two potential polypeptides encoded by MCMV and polypeptides encoded by carnation mottle virus (CarMV) and turnip crinkle virus (TCV). The 25.1 kd ORF most likely encodes the capsid protein. The similar genome organization and amino acid sequence homology of MCMV with CarMV and TCV suggest an evolutionary relationship with these members of the carmovirus group. INTRODUCTION Maize chlorotic mottle virus (MCMV) was first reported in the United States in 1976 when it was associated with maize dwarf mosaic virus or wheat streak mosaic virus in a severe disease in maize termed corn lethal necrosis (CLN)(1). MCMV and its association with these potyviruses in CLN is well characterized ecologically (2,3), epidemiologically (4) and physicochemically (5). However, little information exists concerning the molecular biology of the virus or the mechanism of the synergistic interaction. Previous work (5) has demonstrated a number of properties for MCMV. The virions contain a monopartite RNA genome approximately 4.4 kb in length lacking both 5' genomelinked protein (Vpg) and 3' poly(A) tail. In infected plants, MCMV produces a single, 3' co-terminal 1.3 kb sub-genomic RNA that encodes a 25 kd capsid protein. The 5'end of the virus is capped with a nVGpppA structure. Translation of the MCMV genome