Three distinct DNA ligases in mammalian cells

The major DNA ligase of proliferating mammalian cells, DNA ligase I, catalyzes the joining of single strand breaks in double stranded DNA and is active on a synthetic substrate of oligo(dT) hybridized to poly(dA). DNA ligase I does not catalyze the joining of an oligo(dT).poly(rA) substrate. Two additional DNA ligases, II and III, which can act on the latter substrate have been purified from calf thymus. DNA ligase II, which has been described previously, is a 72-kDa protein. DNA ligase III migrates as a 100-kDa protein in denaturing gel electrophoresis. Structural, immunochemical, and catalytic studies on the three DNA ligase activities strongly indicate that they are the products of three different genes.     

Organization of ribosomal protein genes in Escherichia coli: II. Mapping of ribosomal protein genes by in vitro synthesis of ribosomal proteins using DNA fragments of a transducing phage as templates

The structural genes for six ribosomal proteins (r-proteins) located in the str-spc region around 64 minutes on the Escherichia coli chromosome have been mapped physically with respect to each other and the neighboring genes aroE and trkA. The genes code for the 30 S r-proteins S4 (ram), S5 (spc), S8, S11, S13 and S14. Furthermore, regions coding for unidentified 50 S r-proteins have been indicated.The mapping was performed by biochemical methods employing DNA from the specialized transducing phage λspc1, which carries the aroE-trkA-spc region of the E. coli chromosome. The phage DNA was cleaved by restriction endonucleases, and the generated DNA fragments used as templates for synthesis of r-proteins in a DNA-dependent cell-free system. Since the relative order of the DNA fragments created by the restriction endonucleases is known, a genetic map could be constructed.     

Some rRNA operons in E. coli have tRNA genes at their distal ends.

We have previously isolated seven rRNA operons on plasmids or lambda transducing phages and identified various tRNAs encoded by these operons. Each of the seven operons has one of two different spacer tRNA gene arrangements between the genes for 16S and 23S rRNA: either tRNAGlu2 or both tRNAIle1 and tRNAAla1B genes. In addition, various tRNA genes are located at or near the distal ends of rRNA operons. In particular, genes for tRNATrp and tRNAAsp1 are located at the distal end of rrnC at 83 min on the E. coli chromosome. Experiments with various hybrid plasmids, some of which lack the rRNA promoter, have now demonstrated that this promoter is necessary for expression of the distal tRNA genes. Rifampicin run-out experiments have also provided evidence that the tRNATrp gene is located farther from its promoter than the spacer tRNA gene or the 5S RNA gene. These results confirm the localization of genes for tRNATrp and tRNAAsp1 at the distal end of rrnC and strongly suggest that they are co-transcribed with the genes for 16S, tRNAGlu2, 23S and 5S RNA. Other such distal tRNAs have been identified, and it is suggested that they too are part of rRNA operons.     

Lipoproteomics I: mapping of proteins in low-density lipoprotein using two-dimensional gel electrophoresis and mass spectrometry

The molecular mechanisms underlying the relationship between low-density lipoprotein (LDL) and the risk of atherosclerosis are not clear. Therefore, detailed information about the protein composition of LDL may contribute to reveal its role in atherogenesis and the mechanisms that lead to coronary disease in humans. Here, we sought to map the proteins in human LDL by a proteomic approach. LDL was isolated by two-step discontinuous density-gradient ultracentrifugation and the proteins were separated with two-dimensional gel electrophoresis and identified with peptide mass fingerprinting, using matrix assisted laser desorption/ionization-time of flight-mass spectrometry and with amino acid sequencing using electrospray ionization tandem mass spectrometry. These procedures identified apo B-100, apo C-II, apo C-III (three isoforms), apo E (four isoforms), apo A-I (two isoforms), apo A-IV, apo J and apo M (three isoforms not previously described). In addition, three proteins that have not previously been identified in LDL were found: serum amyloid A-IV (two isoforms), calgranulin A, and lysozyme C. The identities of apo M, calgranulin A, and lysozyme C were confirmed by sequence information obtained after collision-induced dissociation fragmentation of peptides characteristic for these proteins. Moreover, the presence of lysozyme C was further corroborated by demonstrating enriched hydrolytic activity in LDL against Micrococcus lysodeikticus. These results indicate that in addition to the dominating apo B-100, LDL contains a number of other apolipoproteins, many of which occur in different isoforms. The demonstration, for the first time, that LDL contains calgranulin A and lysozyme C raises the possibility that LDL proteins may play hitherto unknown role(s) in immune and inflammatory reactions of the arterial wall.     

Successful immunotherapy with matrix metalloproteinase-derived peptides in adjuvant arthritis depends on the timing of peptide administration

We have recently found that matrix metalloproteinases (MMPs) are targets for T-cell and B-cell reactivity in experimental arthritis. In the present article, we investigate whether modulation of MMP-specific T-cell responses could influence the course of adjuvant arthritis (AA). Lewis rats were treated nasally with MMP peptides prior to or after AA induction. Administration of the MMP-10 or the MMP-16 peptide prior to AA induction reduced the arthritic symptoms. In contrast, administration of the MMP-10 peptide after AA induction aggravated the arthritic symptoms. The present study shows the possible usefulness of MMP peptides for immunotherapy. However, a clear understanding of proper timing of peptide administration is crucial for the development of such therapies.     

Vitamin analysis with use of a yeast electrode

A vitamin B₁ (thiamin)-sensitive electrode has been devised by combining an oxygen electrode with a yeast-containing membrane. The assembly was used for assaying thiamin at concentrations down to 10^?11 gl^?1. The analytical procedure developed should allow the measurement of 10–20 samples per hour. The performance of the yeast electrode was improved when alginate membranes reinforced with a nylon network were used. An apparatus for preparing such membranes is described together with a magnetic membrane holder facilitating handling of membranes in combination with electrodes.     

The distribution of sulphate residues in the chondroitin sulphate chain

1. Electrophoresis of chondroitin sulphate, before and after partial degradation with testicular hyaluronidase, revealed charge heterogeneity of the degraded but not of the intact polymer. 2. Hyaluronidase-treated chondroitin sulphate was fractionated by gel chromatography. Two subfractions which were essentially monodisperse with regard to molecular weight (values of 8600 and 4800, respectively) were separated further by chromatography on Dowex 1. The resulting subfractions differed considerably with respect to their sulphate/disaccharide molar ratios. 3. Amino acid and neutral-sugar analyses of the Dowex 1 subfractions showed that the less sulphated fragments contained the carbohydrate-protein linkage region, whereas the high-sulphated fragments essentially lacked this constituent. It was concluded that chondroitin sulphate contains relatively less sulphate in the vicinity of the carbohydrate-protein linkage region than in the more peripheral portion of the polysaccharide chain.     

Oligomerization and insulin interactions of proinsulin C-peptide: Threefold relationships to properties of insulin

Three principally different sites of action have been reported for proinsulin C-peptide, at surface-mediated, intracellular, and extracellular locations. Following up on the latter, we now find that (i) mass spectrometric analyses reveal the presence of the C-peptide monomer in apparent equilibrium with a low-yield set of oligomers in weakly acidic or basic aqueous solutions, even at low peptide concentrations (sub-μM). It further shows not only C-peptide to interact with insulin oligomers (known before), but also the other way around. (ii) Polyacrylamide gel electrophoresis of C-peptide shows detectable oligomers upon Western blotting. Formation of thioflavin T positive material was also detected. (iii) Cleavage patterns of analogues are compatible with C-peptide as a substrate of insulin degrading enzyme. Combined, the results demonstrate three links with insulin properties, in a manner reminiscent of amyloidogenic peptides and their chaperons in other systems. If so, peripheral C-peptide/insulin interactions, absolute amounts of both peptides and their ratios may be relevant to consider in diabetic and associated diseases.