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Ribosomes from gram-positive Micrococcus luteus contain an acidic protein (ML-S1). ML-S1 has been purified by chromatography of ribosomes on a poly(U)-Sepharose column and the purified protein has a mobility in sodium dodecyl sulphate/polyacrylamide gels similar to that of ribosomal protein SI of Escherichia coil (apparent M1 72000). Protein ML-S1 reacted with E. coil anti-Si serum with an immunological partial-identity reaction. ML-S1 also reacted with antibodies raised against two structural domains of E. coii S1 (the N-terminal ribosome- binding domain and central and C-terminal nucleic-acid-binding domain). Weak reaction with antiserum to the nucleic-acid-binding domain of E. coil SI was observed. ML-S1 was digested with trypsin under mild and exhaustive conditions. Mild digestion resulted in the production of a trypsin-resistant core (ML-SI Fl) like E. coil S1. The fragment pattern obtained after exhaustive digestion differed appreciably from that obtained with E. coil S1. ML-S1 bound to poly(U) as strongly as E. coli S1 and also showed appreciable binding to denatured DNA. Addition of ML-Sl to SI-depleted ribosomes from E. coil and M. luteus markedly stimulated the poly(U)-directed polyphenylalanine synthesis. Phage MS2-RNA-dependent translation was also found to be stimulated by ML-S1 although to a much lesser extent than the stimulation by E. coil S1. At a molar excess of ML-S1 to ribosomes the protein showed a similar inhibitory effect to E. coil S1 on polypeptide synthesis. Our data indicate that ML-S1 retained the structural domains important for its function despite certain structural differences from E. coil S1. [ABSTRACT FROM AUTHOR]

Possible alteration in the ratio of the long and short forms of initiation factor IF-3 (FEBS Lett. 79, 264-275, 1977) during the growth cycle of Escherichia coli was examined. The ratio was found to remain unchanged between the exponential and stationary growth phases. Contrary to an earlier report (Eur. J. Biochem. 29, 319-325, 1972), the total amount of IF-3 relative to the ribosome content in stationary phase cells was essentially the same as in midlogarithrnic phase cells. The activity of IF-3, assayed after its separation from other initiation factors by chromatography, was also the same in extracts from midlogarithmic and stationary phase cells. The data show that in Escherichia coli the ratio of IF-3/ribosome is maintained constant. The ribosomes themselves have been shown to retain virtually full activity in vitro during this transition indicating that growth-cycle-dependent biochemical modifications of the ribosome do not affect its protein synthetic capacity per se. [ABSTRACT FROM AUTHOR]

Escherichia coli ribosomal protein S1 and its mutant, shorter, form m1-S1 were cleaved at internal methionyl residues to yield, respectively, six and five fragments of M1 ranging from 1000 to 24000. Methods are described to isolate the fragments in pure form. Four of the fragments (designated F2a, F2b, F3 and F4) contain between 86 and 215 amino acids and are therefore as large as other ribosomal proteins. Fragment F2a, derived from the N-terminal region, has previously been shown to contain the major ribosome binding domain of S1 [S. Giorginis and A. R. Subramanian (1980) J. Mot Biol. 1411 393 -408]. Here we show that the RNA binding domain of S1 is essentially contained in F3 derived from the middle region of S1 and carrying the nonreactive - SH group. The reactive a SF! group of SI, whose activity is modified by ligand binding, was localized in F2b, a fragment with little RNA binding capacity. The characteristic RNA binding domain and a weak ribosome binding domain of S1 have previously been localized in the large trypsin-resistent core SI-Fl [T. Suryanarayana and A. It Subramanian(1979) J. Mol. Biol. 127, 41-54]. Together these data indicate that two of the key functional domains of SI are located in two regions of the molecule separated by an open, exposed segment. The present study also revealed that the nonreactive - SM group of S1 becomes reactive in m1-S1 by the loss of the remote C-terminal region in the latter. [ABSTRACT FROM AUTHOR]

Structural stability of thermophilic archaeon Sulfolobus acidocaldarius ribosomes, with respect their susceptibility to pancreatic RNase A and stability to temperature (deltaTm), on treatment with various stabilizing (polyamines) and destabilizing (sulfhydryl and intercalating) agents were studied and compared with mesophilic E. coli ribosomes, to understand the structural differences between thermophilic and mesophilic ribosomes. Thermophilic archaeal ribosomes and their subunits were 10-times less susceptible to pancreatic RNase A, compared to mesophilic ribosomes, showing the presence of strong and compact structural organization in them. Thermophilic ribosomes treated with destabilizing agents, such as sulfhydryl reagents [5,5'-Dithio-bis-(2-nitrobenzoic acid), N-ethylmaleimide and p-hydroxymercurybenzoate) and intercalating agents (ethidium bromide, EtBr) showed higher stability to RNase A, compared to similarly treated mesophilic ribosomes, indicating the unavailability of thiol-reactive groups and the presence of strong solvent inaccessible inner core. Higher stability of thermophilic ribosomes compared to mesophilic ribosomes to unfolding agents like urea further supported the presence of strong inner core particle. Thermophilic ribosomes treated with intercalating agents, such as EtBr were less susceptible to RNase A, though they bound to more reagent, showing the rigidity or resilience of their macromolecular structure to alterations caused by destabilizing agents. Overall, these results indicated that factors such as presence of strong solvent inaccessible inner core and rigidity of ribosome macromolecular structure contributed stability of thermophilic ribosomes to RNase A and other destabilizing agents, when compared to mesophilic ribosomes.