Genome resource utilization during prokaryotic development

The distributions of synthesis rates of expressed proteins in a liquid batc h culture of the prokaryote S. coelicolor during 3 days' growth have been a nalyzed by using a law governing the relation between the synthesis rates a nd the corresponding ranks in a list of rates (the so-called simplified can onical law, scl), which we have found previously to characterize the distri bution of prokaryotic protein expression. The scl remains valid throughout development and the two parameters of the distribution, theta and rho, evol ve in a highly characteristic and revealing way. theta is a measure of the degree to which available genomic resources are used, in the sense of explo iting their potential diversity. The passage from one developmental phase t o another is marked by a sharp peak in theta, as these resources are fully mobilized to deal with a crisis (i.e., exhaustion of the habitual food supp ly). This is followed by an even more pronounced trough, as the organism br iefly focuses its resources on synthesizing just those proteins most essent ial for survival, especially those hitherto unavailable and needed for meta bolizing the new nutrient source. The parameter rho indicates redundancy am ong the most abundantly expressed proteins: higher rho corresponds to more diversity; i.e., less duplication of function, hence less robustness. This parameter is relatively steady throughout the development of the culture, e xcept for a pronounced peak during the developmental phase transition. This corresponds to the "emergency mode" characterized by extremely low theta, during which a minimum repertoire of proteins is expressed.