Negative correlation between the abundance of Escherichia coli aminoacyl-tRNA families and their affinities for elongation factor Tu-GTP.

The number of aminoacyl-tRNA molecules in Escherichia coli cells varies by about one order of magnitude from 730 (glutaminyl-tRNA) to 7900 (valyl-tRNA). Relative affinities of E. coli aminoacyl-tRNA for elongation factor Tu-GTP vary also by about one order of magnitude from 2.08 (glutaminyl-tRNA) to 0.15 (valyl-tRNA). The relationship between the abundance of all 20 aminoacyl-tRNA families in 5 E. coli strains and their affinities for elongation factor Tu-GTP was examined by statistical methods. Negative correlation between the two parameters was found. The correlation coefficient was -0.62 to -0.52 with significance level 0.01. Regression analysis give the following formula for the relation between relative abundance of aminoacyl-tRNA families (x) and their relative affinities for elongation factor Tu-GTP (y): y = 1.25 - 0.25x. The analyses indicate that those aminoacyl-tRNA families that are present in cells in low copy number exhibit higher affinity than the more abundant aminoacyl-tRNA families for elongation factor Tu-GTP. The bacterial protein biosynthetic apparatus evolved in such a way as to compensate for a low copy number of some aminoacyl-tRNAs by tight binding of the aminoacyl-tRNA to elongation factor Tu-GTP. This may assure adequate supply of low copy number aminoacyl-tRNAs under conditions of limitation in elongation factor Tu-GTP, e.g. during stringent response, and is consistent with the idea of elongation factor Tu-GTP modulating translational efficiencies of aminoacyl-tRNAs.