Ultracentrifugal studies of the variation with physiological state of the ribosomes in Aerobacter aerogenes

Abstract

Ultracentrifugal studies of ribosomes in extracts of Aerobacter aerogenes cells from logarithmic and stationary growth phases have been undertaken, with the utilization of two different levels of Mg 2+ in preparation of the extracts. Extracts of both log and stationary phase cells examined in 10 −3 M Mg 2+ immediately after cell rupture contained a significant proportion of 70S ribosomes. These dissociated at 0–2 °C to 30S and 50S subunits, apparently following first order kinetics. The initial analyses revealed the following changes upon passage of the cells into the stationary phase: The proportion of 30S and 50S ribosomes was decreased; the proportion of 70S was approximately twice as great in stationary phase as in log phase; and the 100S and polysomes seen in log phase were absent. At the higher concentration of magnesium ion used (8 × 10 −3 M Mg 2+) there was no significant change in ribosome patterns over a period of time in the extracts of either log phase or stationary phase cells. The principal change observed in these experiments upon going from log to stationary phase was disappearance of the polysomes and an increase in the amount of 100S ribosomes. With this higher Mg 2+ level, much less difference in the proportions of 30S, 50S and 70S ribosomes was found between the two growth phases.