A comparison of the alanine-rich sequences of the L7/L12-ribosomal proteins from rat liver, Artemia salina and Escherichia coli, with the amino-terminal region of the alkali light chain A1 from rabbit myosin

Topography and stoichiometry of acidic proteins in large ribosomal subunits from Artemia salina as determined by crosslinking

The 60S subunits isolated from Artemia salina ribosomes were treated with the crosslinking reagent 2-iminothiolane under mild conditions. Proteins were extracted and fractions containing crosslinked acidic proteins were obtained by stepwise elution from CM-cellulose. Each fraction was analyzed by "diagonal" (two-dimensional nonreducing-reducing) NaDodSO4/polyacrylamide gel electrophoresis. Crosslinked proteins below the diagonal were radioiodinated and identified by two-dimensional acidic urea-NaDodSO4 gel electrophoresis. Each of the acidic proteins P1 and P2 was crosslinked individually to the same third protein, P0. The fractions containing acidic proteins were also analyzed by two-dimensional nonequilibrium isoelectric focusing-NaDodSO4/polyacrylamide gel electrophoresis. Two crosslinked complexes were observed that coincide in isoelectric positions with monomeric P1 and P2, respectively. Both P1 and P2 appear to form crosslinked homodimers. These results suggest the presence in the 60S subunit of (P1)2 and (P2)2 dimers, each of which is anchored to P0. Protein P0 appears to play the same role as L10 in Escherichia coli ribosomes and may form a pentameric complex with the two dimers in the 60S subunits.

Sequence homologies in the N-terminal region of the ribosomal 'A' proteins from Methanobacterium Thermoautotrophicum and Halobacterium cutirubrum

The ribosomal 'A' protein from the methanogen, Methanobacterium thermoautotrophicum, has been isolated and purified. The amino acid composition and mobility on two-dimensional gels indicates that this protein shows characteristics similar to the equivalent protein from the extreme halophile, Halobacterium cutirubrum, and is significantly different from the equivalent protein from other bacteria. The first 48 residues of the methanogenic 'A' protein were sequenced and showed a large amount of sequence homology to the H. cutirubrum 'A' protein. When the sequences of these two proteins were compared to the 'A' protein from other procaryotes (eubacteria), much less homology was evident. These results support the hypothesis (Woese, C.R. and Fox, G.F., (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 5088-5090) of two procaryotic lines of evolutionary descent, the eubacteria and the archaebacteria, the latter including the methanogens and the extreme halophiles. The sequence data from the 'A' proteins also indicate that, phylogenetically, the archaebacteria are much closer to the cytoplasmic components of eucaryotes than they are to the eubacteria (or 'true bacteria').

Tropomyosin-like seven residue periodicity in three immunologically distinct streptococal M proteins and its implications for the antiphagocytic property of the molecule

Partial sequences of three immunologically distinct group A streptococcal M proteins (M5, M6, and M24) revealed significant homology with each other, certain amino acid residues being conserved within the three molecules. In addition, a common feature of the sequenced regions of these M proteins was their high alpha-helical potential and the presence of a repeating seven residue periodicity that is characteristic of the double helical coiled-coil molecule, tropomyosin. The existence of a tropomyosin-like seven residue periodicity strongly suggests that regions of these three M proteins may participate in intra- and/or intermolecular coiled-coil interactions. Because of the constraints imposed by such a repeating periodicity, certain conserved residues within the M proteins would occupy spatially equivalent positions in the tertiary structure of these molecules. This common characteristic could play an important role in the common antiphagocytic property of the immunologically diverse M molecules. In addition to similarities in the secondary structure of M proteins and tropomyosin, significant sequence homology has also been observed between certain regions of these molecules with up to 50% identical residues. As a result of the striking structural similarity with tropomyosin, M proteins may play a regulatory role in the contractile mechanisms involved in phagocytosis.

P5/P5' the acidic ribosomal phosphoproteins from Saccharomyces cerevisiae

P5/P5', the most acidic and exchangeable phosphoproteins from the large ribosomal subunit in the yeast Saccharomyces cerevisiae, were purified from the rest of the ribosomal proteins by means of polyacrylamide gel electrophoresis. Antibodies against the pure P5/P5' proteins cross-reacted with polypeptides from the cytoplasm suggesting that a cytoplasmic pool of P5/P5' exist. The cytoplasmic polypeptides immunologically related to P5/P5' are not phosphorylated.

Acidic ribosomal proteins from eukaryotic cells. Effect on ribosomal functions

Precipitation of Saccharomyces cerevisiae ribosomes by ethanol under experimental conditions that do not release the ribosomal proteins can affect the activity of the particles. In the presence of 0.4 M NH4Cl and 50% ethanol only the most acidic proteins from yeast and rat liver ribosomes are released. At 1 M NH4Cl two more non-acidic proteins are lost from the ribosomes. The release of the acidic proteins causes a small inactivation of the polymerizing activity of the particles, additional to that caused by the precipitation itself. The elongation-factor-2-dependent GTP hydrolysis of the ribosomes is, however, more affected by the loss of acidic proteins. These proteins can stimulate the GTPase but not the polymerising activity when added back to the treated particles. Eukaryotic proteins cannot be substituted for bacterial acidic proteins L7 and L12. We have not detected immunological cross-reaction between acidic proteins from Escherichia coli and those from yeast, Artemia salina and rat liver or between acidic proteins from these eukaryotic ribosomes among themselves.

Comparative study between prokaryotes and eukaryotes by chemical iodination of ribosomal proteins

Escherichia coli and Saccharomyces cerevisiae ribosomal proteins were chemically iodinated with 125I by chloramine T under conditions in which the proteins were denatured. The labelled proteins were subsequently separated by two-dimensional gel electrophoresis with an excess of untreated ribosomal proteins from the same species. The iodination did not change the electrophoretic mobility of the proteins as shown by the pattern of spots in the stained gel slabs and their autoradiography. The 125I radioactivity incorporated in the proteins was estimated by cutting out the gel spots from the two-dimensional electrophoresis gel slabs. The highest content of 125I was found in the ribosomal proteins L2, L11, L13, L20/S12, S4 and S9 from E. coli, and L2/L3, L4/L6/S7, L5, L19/L20, L22/S17, L29/S27, L35/L37 and S14/S15 from S. cerevisiae. Comparisons between the electrophoretic patterns of E. coli and S. cerevisiae ribosomal proteins were carried out by coelectrophoresis of labelled and unlabelled proteins from both species. E. coli ribosomal proteins L5, L11, L20, S2, S3 and S15/S16 were found to overlap with L15, L11/L16, L36/L37, S3, S10 and S33 from S. cerevisiae, respectively. Similar coelectrophoresis of E. coli 125I-labelled proteins with unlabelled rat liver and wheat germ ribosomal proteins showed the former to overlap with proteins L1, L11, L14, L16, L19, L20 and the latter with L2, L5, L6, L15, L17 from E. coli.

Isolation and characterization of the acidic phosphoproteins of 60-S ribosomes from Artemia salina and rat liver

Eucaryotic L7/L12-type proteins are present in ethanol/salt extracts (P1 protein) of ribosomes from Artemia salina and rat liver. These proteins are partially phosphorylated and occur in two forms of closely related structure: a major form eL12 having methionine at the N-terminal position and a minor form of eL12 (eL12') which seems slightly elongated and contains a blocked N terminus. Purification of the four different forms of this protein, eL12, eL12-P, eL12' and eL12'-P, was performed by ion-exchange chromatography on carboxymethyl-cellulose and DEAE-cellulose. Using a radioimmuno assay, 1.8 copies of eL12 and 0.9 of eL12' were found on the 80-S A. salina ribosome. In ribosomes of both rat liver and A. salina, eL12 is present in a larger quantity than eL12'. 40-S and 60-S ribosomal subunits extracted with ethanol/salt were essentially free of eL12 proteins. A large pool of eL12 was found in the cytosol after removal of the ribosomes by centrifugation or molecular sieving. The proteins of rat liver and A. salina are similar with regard to their isoelectric points and molecular weights. Sedimentation equilibrium studies indicated that the isolated protein eL12 occurs as a dimer.