Effect of RecF protein on reactions catalyzed by RecA protein.

RecF protein is one of at least three single strand DNA (ssDNA) binding proteins which act in recombination and repair in Escherichia coli. In this paper we show that our RecF protein preparation complexes with ssDNA so as to retard its electrophoretic movement in an agarose gel. The apparent stoichiometry of RecF-ssDNA-binding measured in this way is one RecF molecule for every 15 nucleotides and the binding appears to be cooperative. Interaction of the other two ssDNA-binding proteins, RecA and Ssb proteins, has been studied extensively; so in this paper we begin the study of the interaction of RecF and RecA proteins. We found that the RecF protein preparation inhibits the activity of RecA protein in the formation of joint molecules whether added before or after addition of RecA protein to ssDNA. It, therefore, differs from Ssb protein which stimulates joint molecule formation when added to ssDNA after RecA protein. We found that our RecF protein preparation inhibits two steps prior to joint molecule formation: RecA protein binding to ssDNA and coaggregate formation between ssDNA-RecA complexes and dsDNA. We found that it required a much higher ratio of RecF to RecA protein than normally occurs in vivo to inhibit joint molecule formation. The insight that these data give to the normal functioning of RecF protein is discussed.     

The Evolution of the Y Chromosome with X-Y Recombination

A theoretical population genetic model is developed to explore the consequences of X-Y recombination in the evolution of sex chromosome polymorphism. The model incorporates one sex-determining locus and one locus subject to natural selection. Both loci have two alleles, and the rate of classical meiotic recombination between the loci is r. The alleles at the sex-determining locus specify whether the chromosome is X or Y, and the alleles at the selected locus are arbitrarily labeled A and a. Natural selection is modeled as a process of differential viabilities. The system can be expressed in terms of three recurrence equations, one for the frequency of A on the X-bearing gametes produced by females, one for each of the frequency of A on the X- and Y-bearing gametes produced by males. Several special cases are examined, including X chromosome dominance and symmetric selection. Unusual equilibria are found with the two sexes having very different allele frequencies at the selected locus. A significant finding is that the allowance of recombination results in a much greater opportunity for polymorphism of the Y chromosome. Tighter linkage results in a greater likelihood for equilibria with a large difference between the sex chromosomes in allele frequency.     

Heat shock-related decline in activity and amounts of active elongation factor 1 alpha in ageing and immortal human cells

A significant decline in amount of active elongation factor, EF-1 alpha, and in its catalytic activity was observed in cell-free extracts prepared from normal human diploid fibroblasts (MRC-5) and their SV40-transformed counterparts, after subjecting the cells to 60 min heat shock at different temperatures. Old MRC-5 cells which had become senescent on serial passaging were more sensitive to heat shock-related changes in activity and amounts of active EF-1 alpha than were rapidly proliferating normal and transformed cells.     

Structure and phosphorylation of eukaryotic initiation factor 2. Casein kinase 2 and protein kinase C phosphorylate distinct but adjacent sites in the beta-subunit

Eukaryotic initiation factor 2 (eIF-2) from rabbit reticulocytes can be phosphorylated on its beta-subunit by two different protein kinases, protein kinase C and casein kinase 2. Phosphorylation by these kinases is additive, suggesting that they phosphorylate different sites (serine residues) in eIF-2 beta. Two-dimensional peptide mapping of the phosphopeptides generated from labelled eIF-2 beta by digestion with trypsin, cyanogen bromide or Staphylococcus aureus V8 proteinase showed that protein kinase C and casein kinase 2 phosphorylated distinct and different sites in this protein. This conclusion was supported by the results of analysis of the phosphopeptides on reverse-phase chromatography. Analysis of the phosphopeptides derived from eIF-2 beta labelled by both kinases together strongly suggested that the sites labelled by protein kinase C and casein kinase 2 are adjacent in the primary sequence. These data are discussed in the light of the present understanding of the sequence specificity of the kinases. Rat liver eIF-2 beta was also found to be a substrate for protein kinase C and casein kinase 2, which were again shown to label different serine residues.     

Adhesion-mediating molecules of human monocytes

Adhesion of monocytes to each other and to T cells and substrates is increased by phorbol esters. In the presence of these compounds monocyte aggregation was almost completely inhibited (greater than 90%) by monoclonal antibody 60.3. This antibody recognizes GP90 (CD18), a leukocyte surface glycoprotein which is separately and noncovalently associated to either GP160 (CD11a), GP155 (CD11b), or GP130 (CD11c). Anti-LFA-1 antibody (CD11a) was only partially inhibitory (35%) while antibodies 60.1 (CD11b) and anti-Leu-M5 (CD11c) had a minimal inhibitory effect (10%). Antibody LB-2 recognizing a single glycoprotein distinct from the GP90-GP160 complex and expressed on activated B and T cells, monocytes, and vascular endothelial cells was partially inhibitory (22%). Monoclonal antibodies anti-C3bR (CD35), T29/33 (CD45, leukocyte common antigen 200). TA-1 (CD11a), OKM1 (CD11b), F10-44-2 (brain-leukocyte antigen), OKM5 (monocyte-endothelial cell antigen) and to class I or class II molecules exerted no inhibition on the monocyte aggregation. Fab fragments of antibody 60.3 efficiently inhibited not only monocyte aggregation in the absence or presence of phorbol esters but also adhesion of these cells to autologous or allogeneic T lymphocytes and, to a lesser extent, to plastic surfaces. It is thus concluded that GP90, either alone or associated to the larger glycoproteins, and LB-2 antigen mediate monocyte adhesion.     

cDNA, deduced polypeptide structure and chromosomal assignment of human pulmonary surfactant proteolipid, SPL(pVal)

In hyaline membrane disease of premature infants, lack of surfactant leads to pulmonary atelectasis and respiratory distress. Hydrophobic surfactant proteins of Mr = 5,000-14,000 have been isolated from mammalian surfactants which enhance the rate of spreading and the surface tension lowering properties of phospholipids during dynamic compression. We have characterized the amino-terminal amino acid sequence of pulmonary proteolipids from ether/ethanol extracts of bovine, canine, and human surfactant. Two distinct peptides were identified and termed SPL(pVal) and SPL(Phe). An oligonucleotide probe based on the valine-rich amino-terminal amino acid sequence of SPL(pVal) was utilized to isolate cDNA and genomic DNA encoding the human protein, termed surfactant proteolipid SPL(pVal) on the basis of its unique polyvaline domain. The primary structure of a precursor protein of 20,870 daltons, containing the SPL(pVal) peptide, was deduced from the nucleotide sequence of the cDNAs. Hybrid-arrested translation and immunoprecipitation of labeled translation products of human mRNA demonstrated an Mr = 22,000 precursor protein, the active hydrophobic peptide being produced by proteolytic processing to Mr = 5,000-6,000. Two classes of cDNAs encoding SPL(pVal) were identified. mRNA of approximately 900 bases was identified on Northern analysis of fetal and adult RNA. Human SPL(pVal) mRNA was more abundant in the adult than in fetal lung. The SPL(pVal) gene locus was assigned to chromosome 8.     

Cryptic chemotactic activity of fibronectin for human monocytes resides in the 120-kDa fibroblastic cell-binding fragment

Monocytes and lymphocytes form a second wave of infiltrating blood leukocytes in areas of tissue injury. The mechanisms for monocyte accumulation at these sites are not completely understood. Recently, however, fragments from extracellular matrix proteins including collagen, elastin, and fibronectin have been shown to induce monocyte chemotaxis. In this report we demonstrate that chemotactic activity for human monocytes is expressed when a 120-kDa fragment containing the RGDS cell-binding peptide is released from intact fibronectin or from larger fibronectin fragments. Monocytes, either from mononuclear cell Ficoll-Hypaque preparations (10-20% monocytes, 89-90% lymphocytes) or from elutriation preparations (95% monocytes, 5% lymphocytes), but not lymphocytes, migrated toward 120-kDa fragment preparations (10(-7) M) in blind-end chambers when the cells were separated from the chemoattractant by a 5-micron pore polycarbonate filter either alone or overlying a 0.45-micron pore nitrocellulose filter. Neutrophils migrated toward zymosan-activated serum but not toward 10(-5)-10(-8) M concentrations of the 120-kDa fragment. Intact fibronectin had no chemotactic activity for human monocytes. Fibronectin was isolated from citrated human plasma by sequential gelatin-Sepharose affinity and DEAE ion-exchange chromatography in the presence of buffers containing 1 mM phenylmethylsulfonyl fluoride to prevent fragmentation. Controlled enzymatic digestion with thermolysin cleaved fibronectin into 30 kDa fibrin, 45 kDa collagen, and 150/160-kDa cell and heparin domains. Upon prolonged digestion, purified 150/160-kDa fragments were cleaved into 120-kDa cell and 30/40-kDa heparin-binding fragments. Even though the intact fibronectin molecule, the 150/160-kDa fragments, and the 120-kDa fragment, have cell binding activity for Chinese hamster ovary fibroblasts, only the 120-kDa fragment expressed chemotactic activity for human monocytes. Thus, the 120-kDa fibroblastic cell-binding fragment contains a cryptic site for monocyte chemotaxis which is expressed upon enzymatic cleavage of fibronectin.     

The ionization and distribution behavior of oleic acid in chylomicrons and chylomicron-like emulsion particles and the influence of serum albumin

A reproducible, fairly narrow-sized population of rat lymph chylomicrons, approximately 100 nm, was isolated by centrifugation and combined with low levels of [1-13C]oleic acid for NMR studies. The carboxyl chemical shift was monitored as a function of aqueous pH to characterize the ionization behavior of the fatty acid in these particles. The titration curves were very similar to those for oleic acid in equivalent-sized emulsion particles composed of egg phosphatidylcholine and triolein. A simple partition-ionization model was fitted to the data to derive values for apparent ionization constant, expressed as pKapp, of 7.4-7.5 and the "true" surface to core partition coefficient of approximately 7 for oleic acid in chylomicrons. The fatty acid in chylomicrons thus appeared to be largely associated with the surface regions of these particles. Addition of bovine serum albumin to the samples showed that near physiologic pH much of the fatty acid was bound to the albumin at fatty acid to albumin-binding stoichiometries as high as 5.1 and with mass ratios of greater than 2 in favor of the lipid or lipoprotein particles. Lowering the pH of the medium shifted the distribution of fatty acid away from albumin so that at pH 5 with the emulsion, virtually all the fatty acid was associated with the lipid. The behavior observed under physiologic conditions is consistent with the rapid clearance and redistribution of fatty acid generated in these particles by lipolytic processes. However, under conditions of severe acidosis, hyperlipidemia, and hypoalbuminemia a significant portion of fatty acids might be retained in triglyceride-rich lipoproteins and their remnants and affect subsequent metabolism.     

Structural and conformational features that affect the interaction of polylactosaminoglycans with immobilized wheat germ agglutinin

We examined the interaction between immobilized wheat germ agglutinin and the large, polylactosamine-containing glycans from human erythrocytes and human K-562 erythroleukemic cells. Three classes of interaction were identified. One class of glycan was merely retarded during chromatography. The other two classes were retained and could be distinguished by their ease of displacement with N-acetylglucosamine (GlcNAc); one was a moderate-affinity fraction displaced by 0.1 M GlcNAc and the other was a high-affinity fraction subsequently displaced by 1.0 M GlcNAc. A relatively small fraction of the K-562 polylactosamines were in the high-affinity class. We explored the role that fucose and sialic acid substitutions play in the strength of the lectin-glycan interaction. Although sialic acid is recognized by wheat germ agglutinin, sialylation was not required for the high-affinity interaction, and the presence of sialic acids actually prevented some glycans from binding with high affinity. In contrast, fucose is not part of the binding determinant, yet the removal of fucose resulted in decreased affinity. The possibility that some of these changes in affinity were the result of conformational changes was explored using matrices that had wheat germ agglutinin immobilized at different densities. At low wheat germ agglutinin densities, adult and fetal erythroglycans and K-562 glycophorin-like glycans were not retained by the matrix. As the density increased, the proportion of glycans that were retarded, and ultimately retained, increased. While these increases in the proportions retained occurred in parallel for the three different glycans, the apparent affinities of the glycan-lectin interactions differed. The glycophorin-like glycans were always readily displaced by 0.1 M GlcNAc, even at higher wheat germ agglutinin densities. In contrast, as the wheat germ agglutinin density increased, the proportion of erythroglycans that could be displaced by 0.1 M GlcNAc decreased; at 10 mg/ml immobilized wheat germ agglutinin, greater than 80% of the erythroglycans exhibited this tighter interaction. We suggest that this higher affinity interaction is the result of the large glycans spanning adjacent wheat germ agglutinin molecules, and is determined by the proximity of these molecules and the conformation of the glycans.