Complete nucleotide sequence of the hypervirulent CFH strain of beet curly top virus.

The complete nucleotide sequence of the hypervirulent CFH strain of beet curly top geminivirus (BCTV) has been determined. The circular DNA genome of BCTV-CFH consists of 2,927 nucleotides and shares extensive sequence homology with the biologically distinct California strain of BCTV. Analysis of the CFH nucleotide sequence indicated that the rightward open reading frames (ORFs) R1, R2, and R3 are highly conserved (> 95% amino acid chemical similarity) in the CFH and California strains, although CFH ORF R2 was extended by 24 carboxy-terminal amino acid residues not present in the California strain. The CFH leftward ORFs L1, L2, and L3 shared varying levels of amino acid chemical similarity with the corresponding ORFs of the California strain (78.8, 66.5, and 86.7%, respectively). CFH ORF L4 was the least conserved ORF present in both strains, encoding a 9.9-kDa protein of 87 amino acid residues, which shares 57.6% chemical similarity with 85 carboxy-terminal amino acid residues of the 19.4-kDa ORF L4 of the California strain. The CFH DNA sequence also contained a unique 12.5-kDa ORF (R4); however, there is no evidence to suggest that R4 is expressed. Comparison of the CFH and California strain nucleotide sequences indicates that certain regions of the BCTV genome have diverged, and this divergence may account for differences in the pathogenic properties of the two strains.