Functional inactivation rates of the messenger RNA molecules coding for the individual ribosomal proteins in Escherichia coli.

Summary The rates of functional decay of messenger RNA coding for total soluble, total ribosomal and individual ribosomal proteins were measured in Escherichia coli strain AS-19, at 30^o. This was accomplished by blocking RNA synthesis with the inhibitor thiolutin and measuring residual protein synthesis at various times thereafter. The data obtained expressed as a decay constant (Hartwell and Magasanik, 1963) show that both total soluble and total ribosomal protein decay with similar rates (K₂=0.64 and 0.61 respectively) which are slightly faster than the decay rate of -galactosidse (k₂=0.43) under these conditions. All the individual ribosomal proteins appear to comprise a population of cistrons whose individual mRNA's decay with very similar rates with the possible exception of protein L3, whose mRNA appears consistently to decay very rapidly.Additional data on the stability of the total soluble and total ribosomal proteins during thiolutin treatment (that is, proteins synthesized in the absence of concommitant ribosomal RNA synthesis) fail to demonstrate any marked difference between these two protein populations. Examination of the stability of the individual ribosomal proteins however, reveals that some are degraded up to 35% in 15 min of thiolutin exposure, some to about 15% and some appear to be completely stable. In general, a degree of correlation exists between the stability of a given protein and the observed decay rate of its messenger RNA. This observation may explain in part the spread among the rates of mRNA decay. Nevertheless, we conclude that although degradation is occurring, it is not sufficient to alter the main conclusion that the rates of functional decay of mRNA cistrons coding for the ribosomal proteins are very similar.