I just a read an article, ÒComparative analysis of 1196 orthologous mouse and
human full-length mRNA and protein sequencesÓ by Makalowski W et al (Genome
Research, 9/96; http://22.214.171.124:443/cshl/journals/gr/nih/article.html).
I had been assuming that amino acid sequence conservation (avg 85% between mouse
and human orthologs) would be much higher on average than corresponding
conservation at the nucleic acid level because of redundancy in codon
specification of amino acids. But the authorsÕ analysis reveals that nucleic
acid conservation in the coding sequence also averages 85%.
Is this a surprise to any readers of this newsgroup? Or is my assumption only a
common misconception held among biologists outside the molecular
evolution/comparative genetics realm?
Certainly, this suggests that nucleic acid structure is a way significant
constraint on sequences that are selected for. But would it be fair to see that
mutations selected for because of their effects at the nucleic acid sequence
level may ÔdirectÕ amino acid sequence and hence, protein structure (ie esp. in
cases where nuclei acid sequence conservation is higher than corresponding amino
acid conservation). What mechanism is considered to play such a strong force -
is it the topological structure of the DNA, the way sequence affects its
interaction with histones, the structure and stability of the transcribed RNA?