Identification of the gene encoding the 5S ribosomal RNA maturase in Bacillus subtilis: mature 5S rRNA is dispensable for ribosome function.

Over 25 years ago, Pace and coworkers described an activity called RNase M5 in Bacillus subtilis cell extracts responsible for 5S ribosomal RNA maturation (Sogin & Pace, Nature, 1974, 252:598-600). Here we show that RNase M5 is encoded by a gene of previously unknown function that is highly conserved among the low G + C gram-positive bacteria. We propose that the gene be named rnmV. The rnmV gene is nonessential. B. subtilis strains lacking RNase M5 do not make mature 5S rRNA, indicating that this process is not necessary for ribosome function. 5S rRNA precursors can, however, be found in both free and translating ribosomes. In contrast to RNase E, which cleaves the Escherichia coli 5S precursor in a single-stranded region, which is then trimmed to yield mature 5S RNA, RNase M5 cleaves the B. subtilis equivalent in a double-stranded region to yield mature 5S rRNA in one step. For the most part, eubacteria contain one or the other system for 5S rRNA production, with an imperfect division along gram-negative and gram-positive lines. A potential correlation between the presence of RNase E or RNase M5 and the single- or double-stranded nature of the predicted cleavage sites is explored.

Purification, characterization, and cellular localization of the 100-kDa human placental GTPase-activating protein.

Human placenta contains, in addition to the ubiquitous p120-GTPase-activating protein (GAP), another isoform of 100 kDa, which is specific to this organ. We have established a method for purifying this placental p100-GAP to near homogeneity. The purified p100-GAP allowed the preparation of polyclonal and monoclonal anti Ras-GAP antibodies. Two monoclonal antibodies were selected for a two-site enzyme immunoassay. This simple and accurate assay in turn facilitated the detection of the GAPs during purification. The purified p100-GAP has a specific activity identical to and catalytic properties similar to those of native p120-GAP. Sequence analysis of p100-GAP revealed almost total identity to the known corresponding sequences predicted by the cDNA. The purified p100-GAP kept its activity for 1 year when stored at -80 degrees C. Our immunometric assay showed GAP to be present in human placental extracts at the exceptional abundance of about 0.1% of the total protein content. Quantitative assays showed p100-GAP to be up to 10 times more abundant than p120-GAP. Use of our antibodies allowed the specific localization of placental GAPs to cytotrophoblasts and in the syncytiotrophoblast barrier. Hence p100-GAP is shown to be found only in trophoblasts. The large quantity of p100-GAP in trophoblasts suggests that it may play a regulatory role in the proliferation or the differentiation of this cell type.

High levels of 2',5'-oligoadenylate synthetase and 2',5'-oligoadenylate-dependent endonuclease in human trophoblast.

Human placenta contains a high level of 2',5'-oligoadenylate (2-5A) synthetase activity of the 100-kD form of the enzyme. About 20% of the placental 2-5A synthetase activity was found to be cytosolic, whereas the remaining 80% was released by 0.5 M KCl in the presence of detergent. Most of the enzyme activity was localized in trophoblast cells, which also contain a high level of 2-5A-dependent RNase L activity. The purified trophoblast 100-kD 2-5A synthetase was shown to be activated by human immunodeficiency virus type 1 (HIV-1) 5' RNA 1-311 and 1-707, which both contain the TAR and primer binding site (PBS) structured regions. These two HIV-1 RNAs activated human trophoblast 2-5A synthetase at the same level as poly(I).poly (C), a standard highly efficient activator of the enzyme, and at the same optimal concentration. On the contrary, HIV-1 RNA 311-618, a poorly structured region missing TAR and PBS, was shown to be a poor activator of the enzyme. The specific cellular location of the 2-5A synthetase and its efficient activation by HIV 5' RNA favors the idea that the trophoblast 2-5A system negatively controls HIV replication in trophoblasts.

Differences between some properties of acetylated and nonacetylated forms of HMG1 protein.

There are data suggesting that HMG1 protein may be involved in DNA replication. Recently we have found that only the acetylated form of the protein generates tetramers, stimulates the activity of DNA polymerase alpha (EC 2.7.7.7) (with activated DNA as a template) and forms a specific complex with it. This paper compares some properties of the acetylated and nonacetylated forms of HMG1 protein and shows that it is only the acetylated form which serves as a histone assembly factor, increases the melting temperature of poly d[(A-T)] and stimulates the activity of DNA polymerase alpha when histone H1-depleted chromatin is used as a template.

Acetylated HMG1 protein interacts specifically with homologous DNA polymerase alpha in vitro.

The acetylated, deacetylated and nonacetylated forms of HMG1 proteins from Guerin ascites tumour cells and calf thymus were separated and their in vitro interactions with homologous and heterologous DNA polymerases were studied. It has been found that only the acetylated form of HMG1 proteins forms a specific complex with homologous DNA polymerase alpha and stimulates its activity in vitro. The acetylation therefore is necessary for their possible function in DNA replication. This finding represents an evidence for a relationship between the acetylation of HMG1 proteins and their biological role.

Differences between HMG1 proteins isolated from normal and tumour cells.

The properties of the non-histone chromosomal high-mobility-group 1 (HMG1) proteins from rat liver and Guerin ascites tumour cells (GAT cells) were compared and showed the following differences: (1) five spots were missing in the peptide map of HMG1 from GAT cells in comparison with that of HMG1 from rat liver; (2) HMG1 from GAT cells was about 5-times more poly(ADP)-ribosylated; (3) HMG1 from GAT cells which was found acetylated in vivo and incorporated [14C]acetate in vitro, whereas no incorporation of the label was detected in HMG1 from rat liver; (4) HMG1 from GAT cells exhibited pronounced ability to form oligomers at physiological ionic strength, while HMG1 from rat liver was predominantly in monomeric form. This property of HMG1 from GAT cells was lost upon deacetylation.

Protein HMG1 is different from a DNA helix unwinding protein in calf thymus.

A number of criteria were used--chromatography on columns with single-stranded and double-stranded DNA, electrophoresis, peptide analysis, immunological tests and thermal denaturation of DNA--to show that protein (high mobility group) HMG1 and an unwinding protein from calf thymus are two distinct, unrelated proteins. While both proteins are thought to be related to DNA replication this might involve different mechanisms of action.

Involvement of protein HMG1 in DNA replication.

Antibodies against HMG1 inhibit the incorporation of [3H]thymidine in Ehrlich ascites cell nuclei. By the use of specific inhibitors it is shown that HMG1 is needed for the action of the replicative DNA polymerase and not for the reparative one. This is supported by the fact that the addition of exogenous HMG1 to the nuclei enhances the replication process.

Isolation of high-mobility-group proteins HMG1 and HMG2 in non denaturing conditions and comparison of their properties with those of acid-extracted proteins.

We describe a method for isolation and purification of the chromosomal proteins HMG1 and HMG2 in non-denaturing conditions which overcomes the difficulties of the published methods concerning yield and purity. The method is based on salt extraction, selective precipitation with ammonium sulfate and DEAE-cellulose chromatography. All studied properties of these proteins (formation of protein tetramers, enhancement of micrococcal nuclease digestion of DNA and chromatin, and protection of 165-basepair DNA in chromatosome) differ significantly from the properties of HMG1 and 2 isolated under denaturing conditions.

High mobility group proteins HMG1 and HMG2 do not decrease the melting temperature of DNA.

High mobility group proteins 1 and 2 isolated in non-denaturing conditions cannot decrease the temperature of denaturation of DNA. When they are isolated or treated with tricloroacetic acid a hyperchromic peak below the melting temperature of free DNA appears in agreement with previous data ( Javaherian et al. (1979) Nucl . Acids Res. 6, 3569-3580). We show that this is due to light scattering of aggregated protein at submelting temperatures and not to melting of DNA.

Tissue specificity of tightly bound non-histone chromosomal proteins.

Non-histone chromosomal proteins with high affinity for DNA were isolated from three different rat tissues (liver, spleen and kidney) and were analyzed by SDS-polyacrylamide gel electrophoresis. Each tissue showed a characteristic pattern of missing protein bands and in addition contained at least one unique band. Quantitative differences between the common bands were also observed.

Thermal melting curves of tRNAPhe from yeast lacking different numbers of nucleotides from the 3'-end.

The thermal melting curves of tRNAPhe and tRNALys from yeast lacking different numbers of nucleotides from the 3'-end were recorded. The removal of the first nucleotide had no effect on the melting profile. The stepwise removal of the following six nucleotides caused changes in the character of the derivative melting curves: they became rather broad and melting started at lower temperatures. These results indicate that the nucleotides at the 3'-end contribute to the stability of the molecular structure of tRNAs.