Molecular cloning, sequencing and expression in Escherichia coli of the bean yellow mosaic virus coat protein gene

Abstract

The sequence of 1015 nucleotides from the 3' poly(A) tract of the potyvirus bean yellow mosaic virus (BYMV) RNA has been determined from two cDNA clones. This sequence contained a single long open reading frame (ORF) starting upstream of the cloned region. The ORF was expressed as a fusion protein in Escherichia coli, and the product was detected by antibodies specific for the coat protein of BYMV. The predicted length of the coat protein gene was 822 nucleotides, corresponding to a 273 amino acid coat protein of Mr 30910. The deduced amino acid sequence of the BYMV coat protein was compared to the chemically determined amino acid composition of purified virion protein, and of protein prepared from trypsin-treated virions. The nucleotide and deduced amino acid sequences were compared to the sequences of the coat protein genes of other potyviruses. The BYMV coat protein gene was found to be 50 to 61% homologous to those of other potyviruses at both the nucleotide and amino acid levels; the greatest variation was between the 5'-proximal one-fifth of the genes. Amino acid sequences and hydrophilicity plots of the different potyvirus coat proteins showed similarities which indicated that the structure of the coat protein is highly conserved; a non-terminal region of variability was predicted to be exposed on the exterior of the virion. A putative cleavage site at a glutamine-serine dipeptide was identified by similarity in context to the cleavage sites of tobacco etch virus and tobacco vein mottling virus coat proteins from the viral polyproteins. The BYMV 3'-terminal non-coding region of 166 nucleotides is followed by a poly(A) tract.