|
|
Stanisław Cebrat (Department of Genomics, University of Wrocław)
Optimisation of asymmetric mutational pressure and selection pressure
around the universal genetic code.
Lecture 1 (see Lecture 2, Lecture 3)
|
Abstract:
One of the hypotheses explaining the origin of the genetic code assumes
that its evolution has minimised the deleterious effects of nucleotide
substitutions on the amino acid composition of coded proteins. To estimate
the level of such an optimization of the genetic code it is necessary to
consider the real mutational and selection pressures operating at the
level of genomes and proteomes. Even for the simplest cases of small
bacterial genomes the mutational and selection pressures are different for
genes located on the differently replicating DNA strands: the leading and
lagging ones. Assuming the probability of amino acid substitutions in
proteins as a measure of a code.s susceptibility to errors, it is possible
to calculated the optimal codes for genes located on the leading and
lagging strands separately. The optimal code for genes located on one DNA
strand was simultaneously worse than the universal code for the genes
located on the other strand. Furthermore, only 23 of 20 million random
codes were better than universal one for genes located on both strands
simultaneously while about two orders of magnitude more codes were better
for each of the two strands separately. The result indicates that the
existing universal code, the mutational pressure, the codon and amino acid
compositions are highly optimised for the both differently replicating DNA
strands.
B. Lewin, Genes VIII, Oxford University Press
|
|
