Association of ERK2 mitogen-activated protein kinase with human immunodeficiency virus particles

Here we report the presence of a protein kinase activity associated with human immunodeficiency virus type 1 (HIV-1) particles. We observed phosphorylation of five major proteins by the endogenous protein kinase activity. Phosphoamino acid analysis revealed phosphorylated serine and threonine residues. In addition, we observed autophosphorylation of two proteins in the presence of gamma-ATP in an in-gel phosphorylation assay. These two proteins are not linked by a disulfide bond, suggesting that two different protein kinases are associated with HIV-1 virions. Our results indicate the presence of ERK2 mitogen-activated protein kinase and of a 53,000-molecular-weight protein kinase associated with virions. Moreover, the use of different HIV strains derived from T cells and promonocytic cells, as well as the use of human T-cell leukemia virus type 1 particles, demonstrates that ERK2 is strongly associated with retrovirus particles in a cell-independent manner. Exogenous substrates, such as histone proteins, and a viral substrate, such as Gag protein, are phosphorylated by virus-associated protein kinases.

Two translational initiation sites in the infB gene are used to express initiation factor IF2 alpha and IF2 beta in Escherichia coli

The gene infB codes for the two forms of translational initiation factor IF2: IF2 alpha (97 300 daltons) and IF2 beta (79 700 daltons). To determine whether the two forms differ at their N terminus, purified IF2 alpha and IF2 beta were subjected to 11 or more steps of Edman degradation. The N-terminal amino acid sequences are completely different, but match perfectly the DNA sequences at the beginning of the infB open reading frame and an in-phase region 471 bp downstream. A fusion was constructed between the proximal half of the infB gene and the lacZ gene lacking the region coding for the first eight amino acids. The fused gene expresses two products of 170 000 and 150 000 daltons, corresponding to the fused proteins IF2 alpha-beta-galactosidase and IF2 beta-beta-galactosidase, which confirms in vivo that the IF2 forms differ at their N terminus. A deletion of the 5'-non-translated region of the fused gene, including the Shine/Dalgarno ribosomal binding site, results in the expression of IF2 beta-beta-galactosidase but not IF2 alpha-beta-galactosidase. This strongly suggests that IF2 beta results from independent translation rather than from a precise proteolytic cleavage of IF2 alpha. Further evidence for initiation of protein synthesis at the putative IF2 alpha and IF2 beta start sites was sought by using an in vitro dipeptide synthesis assay. A DNA fragment containing the entire infB gene was cloned into three plasmid vectors and the resulting recombinant DNAs were used as templates in assays containing fMet-tRNA and various labelled aminoacyl-tRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

[Level of polysomes in cells of Escherichia coli treated with sublethal doses of aminoglycosides]

Polysome level was measured in Escherichia coli cells grown in the presence of sublethal doses of four different aminoglycosides which all induce mistranslation: streptomycin, neomycin, kanamycin and gentamycin. No significant variation was noticed as referred to the level of polysomes in normally growing cells. This observation indicates that the erroneous incorporation of amino acids into polypeptide chains does not necessarily result in the release of ribosomes from messenger RNA molecules.

[Protein kinase activity in Escherichia coli]

When growing E. coli in a minimal medium, at least four proteins from the soluble fraction and one ribosome-associated protein are found phosphorylated at the level of their threonine and serine residues.

On the control of ribosomal protein biosynthesis in Escherichia coli. I. Studies on ribosomal protein biosynthesis in amino acid-starved cells

The rate of individual ribosomal protein synthesis relative to total protein synthesis has been determined in Escherichia coli rel+ and rel- cells, under valyltRNA deprivation. These strains have a temperature-sensitive valyl-tRNA synthetase. Starvation was obtained following transfer to the cells to non-permissive temperature. Ribosomal proteins were obtained by treatment of either total lysates of freeze-thawed lysozyme spheroplasts or ammonium sulphate precipitate of ribosomes, with acetic acid. Differential labelling of the ribosomal proteins was observed in both strains: proteins from the rel+ strain appear more labelled than those from the rel- strain, the rate of labelling of individual proteins being about the same in both strains. Moreover ribosomal proteins were found as stable during starvation as total protein. It is thus concluded that in starving cells individual ribosomal proteins are not synthesized at equal rates. This indicates that the synthesis of ribosomal proteins is not only under the control of the rel gene.

Cross-linking of initiation factor IF-2 to Escherichia coli 30 S ribosomal proteins with dimethylsuberimidate

The 30 S ribosomal proteins near the binding site for initiation factor IF-2 in Escherichia coli were identified by allowing complexes of 30 S subunits, [32P]phosphoryl initiation factor IF-2 and nonradioactive initiation factors IF-1 and IF-3, to react with the protein cross-linking reagent dimethylsuberimidate. Noncross-linked initiation factors were removed by centrifugation of the complexes in buffer containing a high salt concentration; the protein was extracted from the pelleted particles; and cross-linked species containing initiation factor IF-2 and ribosomal proteins were partially purified by column chromatography on Sephadex G-75. The mixture of cross-linked products was analyzed by radioimmunodiffusion with antisera prepared against 20 individual 30 S ribosomal proteins S1, S2, S11, S12, S13, S14, and S19 was interpreted to mean that initiation factor IF-2 was present in covalent cross-linked complexes containing those proteins. The results imply that these 30 S ribosomal proteins are near the binding site for initiation factor IF-2.