The complete nucleotide sequence (8024 nucleotides) of the circular double-stranded DNA of cauliflower mosaic virus has been established. The DNA molecule is known to possess three discrete single-stranded discontinuities, often referred to as "gaps," two in one strand and one in the other. The sequence data indicate that gap 1, the single discontinuity in the alpha strand, corresponds to the absence of no more than one or two nucleotides with respect to the complementary beta strand. The two discontinuities in the beta strand, however, are not authentic gaps since no nucleotides are missing, but are instead regions of sequence overlap: a short sequence (19 residues for gap 2, t least 2 residues for gap 3) at one terminus of each discontinuity, probably the 5' terminus, is displaced from the double helix by an identical sequence at the other boundary of the discontinuity. Analysis of the distribution of nonsense codons in the DNA sequence is consistent with other evidence that only the alpha strand is transcribed. The coding region extends around the circular molecule from 4 map units of gap 1, the map origin, to map position 91, and consists of six long open reading frames. Our findings suggest, but do not prove, that the DNA sequence of the open reading frames is colinear with viral protein sequences. The cistron for the viral coat protein, which is probably synthesized in the form of a precursor, has been situated in coding region IV on the basis of its unusual amino acid composition.

A comparative study of the aminoacylation of the two RNA components of turnip yellow mosaic virus, of yeast tRNA""', tRNAP' and of tRNAPhe by purified yeast valyl-tRNA synthetase is reported. Aminoacylations were performed in the presence of pure yeast tRNA nucleotidyltransferase, since 85 "/, of the viral RNA molecules lacked the 3'-adenosine. We find that aminoacylation of the viral RNAs, like tRNA aminoacylation, reflects an equilibrium between the acylation and deacylation reactions. The kinetic parameters of TY M virus RNA valylation resemble the values found for tRNA""' valylation; in particular, there is a strong affinity between the viral RNA and valyl-tRNA synthetase and the rate constant for TYM virus RNA valylation is only slightly lower than that for tRNAV"'. This result contrasts with the reduced rates observed in tRNA mischarging, and suggests that the viral RNA could be easily aminoacylated in vivo. Considering the fact that the 3'-terminal sequence of TYM virus RNA has only a few points of resemblance to a tRNA sequence, we propose that there are some structural motifs found in both tRNA""' and TYM virus RNA which are brought in a similar spatial arrangement recognized by valyl-tRNA synthetase.