Nucleotide sequence of DNA from an altered-virulence isolate D/H of the cauliflower mosaic virus

The double-stranded DNA from the isolate D/H with an altered virulence of the cauliflower mosaic virus (CaMV) contains 8016 bp. The DNA is circular and possesses, like the DNA of most CaMV strains, three sequence interruptions. The comparison of its sequence with the previously published sequences of two other CaMV strains (Cabb-S and CM 1841) leads to the following conclusions: (1) The genetic organization of all three CaMV strains is identical with six potential genes (open reading frames) and two intergenic regions; (2) considered pairwise, the three DNAs differ from one another by only about 5% with base substitutions accounting for most of the changes although several deletions and insertions are also observed. The sequence differences among the three strains are spread in a uniform manner upon the genome except for the two intergenic regions, which are more highly conserved. The stability of the noncoding regions is probably linked to the fact that they carry sequences important for the initiation and termination of transcription. On the other hand, the sequence variation in the open reading frames has relatively little effect on the sequence of the corresponding polypeptides as changes occur preferentially in the third position of the reading frame triplets. It is anticipated that knowledge of the DNA sequences of several CaMV strains will facilitate construction of inter-strain recombinants which, once available, can be used to correlate gene structure and function.