Crick Wobble and Superwobble in Standard Genetic Code Evolution.

Wobble coding is inevitable during evolution of the Standard Genetic Code (SGC). It ultimately splits half of NN U/C/A/G coding boxes with different assignments. Further, it contributes to pervasive SGC order by reinforcing close spacing for identical SGC assignments. But wobble cannot appear too soon, or it will inhibit encoding and more decisively, obstruct evolution of full coding tables. However, these prior results assumed Crick wobble, NN U/C and NN A/G, read by a single adaptor RNA. Superwobble translates NN U/C/A/G codons, using one adaptor RNA with an unmodified 5' anticodon U (appropriate to earliest coding) in modern mitochondria, plastids, and mycoplasma. Assuming the SGC was selected when evolving codes most resembled it, characteristics of the critical selection events can be calculated. For example, continuous superwobble infrequently evolves SGC-like coding tables. So, continuous superwobble is a very improbable origin hypothesis. In contrast, late-arising superwobble shares late Crick wobble's frequent resemblance to SGC order. Thus late superwobble is possible, but yields SGC-like assignments less frequently than late Crick wobble. Ancient coding ambiguity, most simply, arose from Crick wobble alone. This is consistent with SGC assignments to NAN codons.