Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus.

A novel penicillin-binding protein, PBP-2' (Mr about 75,000), is known to be induced in excessively large amount by most beta-lactam compounds in cells of a clinically isolated strain of Staphylococcus aureus, TK784, that is highly resistant to beta-lactams and also most other antibiotics. This protein has very low affinities to most beta-lactam compounds and has been supposed to be the cause of the resistance of the cells to beta-lactams. A 14-kilobase DNA fragment was isolated from the cells that carried the gene encoding this penicillin-binding protein and also a genetically linked marker that is responsible for the resistance to tobramycin. This DNA was cloned on plasmid pACYC184 and was shown to cause both production of PBP-2' and resistance to tobramycin in Escherichia coli cells. However, the formation of PBP-2' in E. coli was only moderate and was independent of normal inducer beta-lactams. The PBP-2' formed in the E. coli cells showed slow kinetics of binding to beta-lactams similar to that of PBP-2' formed in the original S. aureus cells and gave a similar pattern of peptides to the latter when digested with the proteolytic V8 enzyme of S. aureus.     

Purification and properties of epithelial growth inhibitor (EGI) from human platelets: its separation from type beta transforming growth factor (TGF-beta)

We previously reported that sera from various kinds of animals contain a protein(s) capable of inhibiting the growth of the non-malignant epithelial cell line derived from Buffalo rat liver (BRL). In the present study, a similar epithelial cell-specific growth inhibitor (EGI) was purified to homogeneity from an acid-ethanol extract of human platelets. During purification, EGI was separated from the major component of type beta transforming growth factor (TGF-beta), which can stimulate the colony formation of the non-malignant fibroblastic cell line derived from rat kidney (NRK) in soft agar in the presence of epidermal growth factor (EGF). The purified EGI had an Mr of 27,000, and was composed of two subunits identical in Mr. It significantly inhibited the growth in monolayer cultures of three non-malignant epithelial cell lines, BRL, MDCK (from Madin-Darby canine kidney) and BSC-1 (from African green monkey kidney), at doses lower than 40 pg/ml in medium containing 10% fetal calf serum. Its inhibitory activity was stable against heating at 90 degrees C for 3 min, but not against treatment with 50 mM dithiothreitol. In addition, TGF-beta was also partially purified from the same extract. The purified TGF-beta did not show any inhibitory activity toward the growth of BRL, MDCK, BSC-1, or NRK.     

Reactivity of a sulfhydryl group of the ras oncogene product p21 modulated by GTP binding

We have studied the sensitivity of sulfhydryl groups of a highly purified p21 protein of the v-rasH oncogene to a thiol-specific reagent, N-ethylmaleimide (NEM). Approximately 70% of GTP binding and autokinase activities of p21 were inactivated by NEM, and excessive amounts of GTP or GDP protected p21 activities. Thiol titration revealed the presence of one fast reactive cysteine residue, the susceptibility of which is modulated by GTP binding. A total of 4 and 6 residues, respectively, became titratable upon denaturation and reduction, suggesting the presence of a disulfide bond. This GTP-modulated sulfhydryl group was identified as Cys-80 in the following tryptic peptide sequence: NH2-Thr-Gly-Glu-Gly-Phe-Leu-Cys-Val-Phe-Ala-Ile-Asn-Asn-Thr-Lys-COOH. This is based on the comparative tryptic peptide mapping of [14C]NEM-modified p21 in the presence and absence of GTP. The GTP-modulated peptide co-chromatographed with a synthetic peptide of the predicted sequence. Amino acid analysis of the purified [14C]NEM-modified peptide from tryptic digests of p21 also confirmed its identity. This region of p21 shares an extensive sequence homology with various G-proteins and appears to be in the vicinity of the GTP-binding domain of these proteins.     

Possible involvement of aminopeptidase, an ecto-enzyme, in the inactivation of bradykinin by intact neutrophils

The subcellular localization of the bradykinin-inactivating activity was studied using guinea-pig neutrophils and the following results were obtained. The bradykinin-inactivating activities were found to be present in the cytosol and membrane fractions but not in the granular and nuclear fractions. The bradykinin-inactivating activity of the cytosol fraction was inhibited by N-carbobenzoxy-Gly-Pro, an inhibitor of prolyl endopeptidase, whereas that of the membrane fraction was inhibited by bestatin, an inhibitor of aminopeptidase. Prolyl endopeptidase and aminopeptidase activities were located predominantly in the cytosol and membrane fractions, respectively, and their activities were inhibited by their respective inhibitors. Prolyl endopeptidase and aminopeptidase activities measured with synthetic substrates were competitively inhibited by bradykinin, suggesting that bradykinin is a possible substrate for prolyl endopeptidase and aminopeptidase. Intact neutrophils inactivated bradykinin rapidly. However, when neutrophils were modified chemically by diazotized sulfanilic acid, a poorly permeant reagent which inactivates ecto-enzymes selectively, both the bradykinin-inactivating activity and aminopeptidase activity of neutrophils decreased significantly without any inhibition of cytosol prolyl endopeptidase. The possibility that aminopeptidase, an ecto-enzyme, would be responsible for the inactivation of bradykinin by intact neutrophils was deduced from the results above, although both cytosol prolyl endopeptidase and membrane aminopeptidase could inactivate bradykinin.     

The structures of the carbohydrate moieties of mouse kidney gamma-glutamyltranspeptidase: occurrence of X-antigenic determinants and bisecting N-acetylglucosamine residues

Paper electrophoresis and Bio-Gel P-4 column chromatography of the oligosaccharides released from mouse kidney gamma-glutamyltranspeptidase by hydrazinolysis gave fractionation patterns quite distinct from those of the bovine and rat kidney enzymes. Structural studies of the fractionated oligosaccharides by sequential exoglycosidase digestion in combination with methylation analysis showed that mouse kidney gamma-glutamyltranspeptidase contains a series of bisected complex-type asparagine-linked sugar chains with the following oligosaccharides as their outer chain moieties: GlcNAc beta 1----, Sia alpha 2----Gal beta 1----4GlcNAc beta 1----, Gal beta 1----4(Fuc alpha 1----3)GlcNAc beta 1----, and sialylated N-acetyllactosamine repeating sugar chains. Some of these sugar chains were found for the first time in glycoproteins.     

Polymorphic extracellular glucoamylase genes and their evolutionary origin in the yeast Saccharomyces diastaticus.

DNA coding for extracellular glucoamylase genes STA1 and STA3 was isolated from DNA libraries of two Saccharomyces diastaticus strains, each carrying STA1 or STA3. Cells transformed with a plasmid carrying either the STA1 or STA3 gene secreted glucoamylases having the same enzymatic and immunological properties and the same electrophoretic mobilities in acrylamide gel electrophoresis as those of authentic glucoamylases. Southern blot analysis of genomic DNA from S. diastaticus and a glucoamylase-non-secreting yeast, Saccharomyces cerevisiae, revealed that the STA1 and STA3 loci of S. diastaticus showed a high degree of homology, and that both yeast species (S. diastaticus and S. cerevisiae) contained DNA segments highly homologous to those of the extracellular glucoamylase genes. Restriction maps of the homologous DNA segments suggested that the extracellular glucoamylase genes of S. diastaticus may have arisen from recombination among the resident DNA segments in S. cerevisiae.     

Nucleotide sequence of the extracellular glucoamylase gene STA1 in the yeast Saccharomyces diastaticus.

The complete nucleotide sequence of the extracellular glucoamylase gene STA1 from the yeast Saccharomyces diastaticus has been determined. A single open reading frame codes for a 778-amino-acid protein which contains 13 potential N-glycosylation sites. In the 5'- and 3'-flanking regions of the gene, there are striking sequence homologies to the corresponding regions of ADH1 for alcohol dehydrogenase and MAT alpha 2 for mating type control in the yeast Saccharomyces cerevisiae. The putative precursor begins with a hydrophobic segment that presumably acts as a signal sequence for secretion. The presumptive signal sequence showed a significant homology to that of Bacillus subtilis alpha-amylase precursor. The next segment, of ca. 320 amino acids, contains a threonine-rich tract in which direct repeat sequences of 35 amino acids exist, and is bordered by a pair of basic amino acid residues (Lys-Lys) which may be a proteolytic processing signal. The carboxy-terminal half of the precursor is a presumptive glucoamylase which contains several peptide segments showing a high degree of homology with alpha-amylases from widely diverse organisms including a procaryote (B. subtilis) and eucaryotes (Aspergillus oryzae and mouse). Analysis of both the nucleotide sequence of the STA1 gene and the amino acid composition of the purified glucoamylase suggested that the putative precursor is processed to yield subunits H and Y of mature enzyme by both trypsin-like and chymotrypsin-like cleavages.     

An improved technique for dissociating hepatocytes from fixed mouse liver for cytochemistry

A refined version of a method described previously for dissociating hepatocytes from fixed liver is described. The objective was to develop a procedure that would dispense with the postosmication of previously fixed tissue. In the new procedure fixed liver blocks are wrapped with a quadruple layer of nylon cloth, and, by squeezing them in a buffer solution, individually dissociated cells pass through the cloth without significant damage. The procedure makes it possible to dissociate liver tissue fixed with modified Karnovsky's fixative, Zamboni's fixative or cacodylate buffered glutaraldehyde. The subsequent compatibility of the single cells obtained with many cytochemical procedures has been confirmed.     

Characterization of a growth-inhibiting protein present in rat serum that exerts a differential effect onin vitro growth of nonmalignant rat liver cells when compared with Rous sarcoma virus-transformed rat liver cells

Summary We have previously reported the transformation by Rous sarcoma virus of a cloned epithelial cell line (BRL) established from Buffalo rat liver by H. Coon. The nontransformed (BRL) and transformed (RSV-BRL) cells grew at comparable rates in culture, whereas only the transformed cells were tumorigenic in vivo. We report here on the existence in rat and mouse sera of a growth inhibitor for the nontransformed BRL cells. The transformed BRL cells (RSV-BRL) were insensitive to this inhibitor. The inhibitory activity was not prominent in sera from other species of animals tested except for rabbit; this serum inhibited the growth of RSV-BRL cells more strongly than that of BRL cells. The growth inhibitor was partially purified from rat serum. It is a protein free of lipid and has a molecular weight of about 220 000. The inhibitor could be separated into three components of pI 4.6, 5.2 (major) and 5.6 by isoelectric electrophoresis. EDITOR'S STATEMENT Although compelling theoretical arguments sometimes can be made for the likely existence of growth-inhibitory substances of physical relevance in the control of cell proliferation, experiments aimed at identifying and studying such factors often are difficult to design and interpret, and little strong data exists to suggest that growth-inhibitory substances are important regulatorsin vivo. The information presented in this paper represents a start toward developing a useful system for studying growth-inhibitory factor. David W. Barnes     

Possible role of prostaglandin F in blastocyst implantation

The synthesis and release of Prostaglandin F (PGF) by the rabbit blastocyst and endometrium were investigated on Day 6 and Day 7, using radioimmunoassay, autoradiography and conversion experiments. The following results were obtained: The content of PGF in the blastocyst increased significantly (P less than 0.01) from Day 6 to Day 7. The content of PGF in the endometrium was significantly higher (P less than 0.05) on Day 7 implantation sites compared to the other areas. The in vitro synthesis and release of PGF by Day 6 blastocysts sharply increased after one and two hours of culture, respectively. Thereafter both values declined with time. The in vitro synthesis and release of PGF by Day 6 endometria increased continuously with time. 14C-arachidonic acid (14C-AA) was incorporated into Day 6 blastocysts in vitro and converted to PGF2 alpha. These results suggest that both the endometrium and the blastocyst are the sources of the PGs involved in implantation, and that PGF derived from the blastocysts may act as the trigger of implantation.