Extent of variation in three related bacteriophage RNA molecules

Abstract

The isolation and sequence analysis of a series of oligonucleotides from complete ribonuclease T 1 digests of bacteriophage R17 RNA have been reported (Jeppesen, 1971). We have obtained the homologous sets of large T 1-resistant oligonucleotides from the related phages f2 and MS2. As expected from earlier findings (Nichols & Robertson, 1971), each RNA can be uniquely characterized by its ribonuclease T 1 fingerprint. Comparison of nucleotide sequences from the sets of RNA fragments from R17, f2 and MS2 allows an estimate of the over-all degree of variation among the three RNA's (2.8 to 3.4%), and yields additional evidence that non-coding regions show significantly lower variation. R17, f2 and MS2 are apparently not linear descendants, but could have diverged from a common ancestor. Base substitutions involving U and C transitions occur at a higher frequency than would be expected on a random basis. It appears probable that a total of 15 to 20 base replacements in the phage coat protein cistron may accompany the single amino-acid difference between f2 coat protein and that of either R17 or MS2. We conclude that analysis of this sort should prove useful in determining the extent of variation among members of any set of closely related nucleic acid molecules.