Pressures in archaeal protein coding genes: a comparative study.

Our studies on the bases of codons from 11 completely sequenced archaeal genomes show that, as we move from GC-rich to AT-rich protein-coding gene-containing species, the differences between G and C and between A and T, the purine load (AG content), and also the overall persistence (i.e. the tendency of a base to be followed by the same base) within codons, all increase almost simultaneously, although the extent of increase is different over the three positions within codons. These findings suggest that the deviations from the second parity rule (through the increasing differences between complementary base contents) and the increasing purine load hinder the chance of formation of the intra-strand Watson-Crick base-paired secondary structures in mRNAs (synonymous with the protein-coding genes we dealt with), thereby increasing the translational efficiency. We hypothesize that the ATrich protein-coding gene-containing archaeal species might have better translational efficiency than their GC-rich counterparts.