Amino-acid Sequence Invariance and Genetic Code

FROM the complete nucleotide sequence of the gene coding for the coat protein of coliphage MS2, Min Jou et al.¹ have suggested a scheme for base-pairing between certain stretches of the polynucleotide chain. Their hypothesis leads to the formation of double helices in their “flower” model and to the consequent implication that nucleic acids have a well-defined tertiary structure. Such a scheme remains to be proved by direct observation of the structure, but the indirect arguments of Min Jou et al. and others appear so convincing and the notion that the genetic material has a definite tertiary structure seems so probable, that there can be little doubt that the “flower” model is on the right lines in principle, even though it may be incorrect in detail.