Zipf-like behavior in procaryotic protein expression

The relative rates of synthesis p(r) of proteins present in various procary otic organisms have been found to follow the simple canonical law p(r) simi lar to(r + rho)(-1/theta), where r is the rank. The parameter rho is interp reted as the bias characterizing the mode of control (i.e., the overall pre ference for positive or negative control) of gene expression. By analogy wi th thermodynamics, and drawing parallels with the abstract theory of messag es, theta is the informational temperature, which characterizes the extent to which the organism's genome is used to produce proteins. The quantity of selective information H (analogous to thermodynamic entropy) was calculate d for the distribution of synthesis rates using Shannon's formula. For all the organisms investigated, H was approximately 8 bits/protein. [S1063-651X (98)14512-9].