INFLUENCE OF GENOMIC G-ACID-COMPOSITION OF PROTEINS FROM 59 BACTERIALSPECIES(C CONTENT ON AVERAGE AMINO)

The amino-acid composition of 23 490 proteins from 59 bacterial specie s was analyzed as a function of genomic G + C content. Observed amino- acid frequencies were compared with those expected from a neutral mode l assuming the absence of selection on average protein composition. In tegral membrane proteins and non-integral membrane proteins were analy zed separately. The average deviation from this neutral model shows th at there is a selective pressure increasing content in charged amino a cids for non-integral membrane proteins, and content in hydrophobic am ino acids for integral membrane proteins. Amino-acid frequencies were greatly influenced by genomic G + C content, but the influence was fou nd to be often weaker than predicted. This may be evidence for a selec tive pressure, maintaining most amino-acid frequencies close to an opt imal value. Concordance between the genetic code and protein compositi on is discussed in the light of this observation. (C) 1997 Elsevier Sc ience B.V.