Affiliations: School of Public Health, University of Texas, Houston,
TX 77030, USA | Beckman Research Institute of the City of Hope,
Duarte, CA 91010, USA
Abstract: The updated structural and phylogenetic analyses of tRNA pairs with
complementary anticodons provide independent support for our earlier finding,
namely that these tRNA pairs concertedly show complementary second bases in the
acceptor stem. Two implications immediately follow: first, that a tRNA molecule
gained its present, complete, cloverleaf shape via duplication(s) of a
shorter precursor. Second, that common ancestry is shared by two major
components of the genetic code within the tRNA molecule – the classic code
per se embodied in anticodon triplets, and the operational code of
aminoacylation embodied primarily in the first three base pairs of the acceptor
stems. In this communication we show that it might have been a double,
sense-antisense, in-frame translation of the very first protein-encoding genes
that directed the code's earliest expansion, thus preserving this fundamental
dual-complementary link between acceptors and anticodons. Furthermore, the dual
complementarity appears to be consistent with two mirror-symmetrical modes by
which class I and II aminoacyl-tRNA synthetases recognize the cognate tRNAs –
from the minor and major groove side of the acceptor stem, respectively.
