HYDROPHOBICITY, EXPRESSIVITY AND AROMATICITY ARE THE MAJOR TRENDS OF AMINO-ACID USAGE IN 999 ESCHERICHIA-COLI CHROMOSOME-ENCODED GENES

Multivariate analysis of the amino-acid compositions of 999 chromosome -encoded proteins from Escherichia coli showed that three main factors influence the variability of amino-acid composition. The first factor was correlated with the global hydrophobicity of proteins, and it dis criminated integral membrane proteins from the others. The second fact or was correlated with gene expressivity, showing a bias in highly exp ressed genes towards amino-acids having abundant major tRNAs. Just as highly expressed genes have reduced codon diversity in protein coding sequences, so do they have a reduced diversity of amino-acid choice. T his showed that translational constraints are important enough to affe ct the global amino-acid composition of proteins. The third factor was correlated with the aromaticity of proteins, showing that aromatic am ino-acid content is highly variable.