Molecular and functional properties of protein SS1 from small ribosomal subunits of Streptomyces aureofaciens

Probing the relationship between Gram-negative and Gram-positive S1 proteins by sequence analysis

Escherichia coli ribosomal protein S1 is required for the translation initiation of messenger RNAs, in particular when their Shine-Dalgarno sequence is degenerated. Closely related forms of the protein, composed of the same number of domains (six), are found in all Gram-negative bacteria. More distant proteins, generally formed of fewer domains, have been identified, by sequence similarities, in Gram-positive bacteria and are also termed 'S1 proteins'. However in the absence of functional information, it is generally difficult to ascertain their relationship with Gram-negative S1. In this article, we report the solution structure of the fourth and sixth domains of the E. coli protein S1 and show that it is possible to characterize their beta-barrel by a consensus sequence that allows a precise identification of all domains in Gram-negative and Gram-positive S1 proteins. In addition, we show that it is possible to discriminate between five domain types corresponding to the domains 1, 2, 3, 4-5 and 6 of E. coli S1 on the basis of their sequence. This enabled us to identify the nature of the domains present in Gram-positive proteins and, subsequently, to probe the filiations between all forms of S1.

Expression of the Csp protein family upon cold shock and production of tetracycline in Streptomyces aureofaciens

A shift down in temperature causes in Streptomyces aureofaciens a transient repression of polypeptide synthesis. During the acclimation phase 32 proteins were synthesized. The addition of tetracycline (200 microg/ml) to cells from exponential phase of growth leads to induction of 27 novel proteins and 17 upregulated proteins migrated in 2-D gel as proteins expressed upon cold shock. Immunoblot analysis using antibodies raised against CspB, CspC, and CspD of Bacillus subtilis revealed five cross-reactive proteins of the Csp family. Proteins CspB and CspD are predominantly induced at low temperature or by the presence of tetracycline. Expression of Csp proteins during the acclimation phase is regulated on the transcription level. Proteins of the Csp family have been shown to be associated with ribosomes and can be removed by 1 M NH(4)Cl. As expression of Csp proteins differs during development or temperature shift down, these proteins can be considered as trans-acting factors to form contacts with the coding region of specific mRNAs.

Protein synthesis in vitro by Micrococcus luteus

Bacillus subtilis and related gram-positive bacteria which have low to moderate genomic G + C contents are unable to efficiently translate mRNA derived from gram-negative bacteria, whereas Escherichia coli and other gram-negative bacteria are able to translate mRNA from both types of organisms. This phenomenon has been termed translational species specificity. Ribosomes from the low-G + C-content group (low-G + C group) of gram-positive organisms (B. subtilis and relatives) lack an equivalent to Escherichia ribosomal protein S1. The requirement for S1 for translation in E. coli (G. van Dieijen, P. H. van Knippenberg, J. van Duin, B. Koekman, and P. H. Pouwels, Mol. Gen. Genet. 153:75-80, 1977) and its specific role (A.R. Subramanian, Trends Biochem. Sci. 9:491-494, 1984) have been proposed. The group of gram-positive bacteria characterized by high genomic G + C content (formerly Actinomyces species and relatives) contain S1, in contrast to the low-G + C group (K. Mikulik, J. Smardova, A. Jiranova, and P. Branny, Eur. J. Biochem. 155:557-563, 1986). It is not known whether members of the high-G + C group are translationally specific, although there is evidence that one genus, Streptomyces, can express Escherichia genes in vivo (M. J. Bibb and S. N. Cohen, Mol. Gen. Genet. 187:265-277, 1985; J. L. Schottel, M. J. Bibb, and S. N. Cohen, J. Bacteriol. 146:360-368, 1981). In order to determine whether the organisms of this group are translationally specific, we examined the in vitro translational characteristics of a member of the high-G + C group, Micrococcus luteus, whose genomic G + C content is 73%. A semipurified coupled transcription-translation system of M. luteus translates Escherichia mRNA as well as Bacillus and Micrococcus mRNA. Therefore, M. luteus is translationally nonspecific and resembles E. coli rather than B. subtilis in its translational characteristics.

Structural and immunochemical characterization of a ribosomal protein from gram-positive Micrococcus luteus which is functionally homologous to Escherichia coli ribosomal protein S1

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 S1 of Escherichia coli (apparent Mr 72,000). Protein ML-S1 reacted with E. coli anti-S1 serum with an immunological partial-identity reaction. ML-S1 also reacted with antibodies raised against two structural domains of E. coli 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. coli S1 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-S1F1) like E. coli S1. The fragment pattern obtained after exhaustive digestion differed appreciably from that obtained with E. coli S1. ML-S1 bound to poly(U) as strongly as E. coli S1 and also showed appreciable binding to denatured DNA. Addition of ML-S1 to S1-depleted ribosomes from E. coli 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. coli S1. At a molar excess of ML-S1 to ribosomes the protein showed a similar inhibitory effect to E. coli S1 on polypeptide synthesis. Our data indicate that ML-S1 retained the structural domains important for its function despite certain structural differences from E. coli S1.