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Biomedical subjects

M Riley

Publications and source records attributed to M Riley.

At least 109 records · Page 6Linked to original sources
PubMed1985

Nucleotide sequence of Klebsiella pneumoniae lac genes.

The nucleotide sequences of the Klebsiella pneumoniae lacI and lacZ genes and part of the lacY gene were determined, and these genes were located and oriented relative to one another. The K. pneumoniae lac operon is divergent in that the lacI and lacZ genes are oriented head to head, and complementary strands are transcribed. Besides base substitutions, the lacZ genes of K. pneumoniae and Escherichia coli have suffered short distance shifts of reading frame caused by additions or deletions or both during evolutionary divergence from a common ancestral gene. Relative to corresponding E. coli sequences, the nucleotide sequences of the lacZ and lacY genes are 61 and 67% conserved, and the lacI genes are 49% conserved. A comparison of both nucleotide and amino acid sequences revealed that the K. pneumoniae and E. coli lacI genes and lac repressor proteins each are related to the galR gene and gal repressor of E. coli to about the same extent. In terms of evolutionary relationships, the divergence of the forerunner of the galR gene from an ancestral lac repressor gene preceded separation and differentiation of the K. pneumoniae and E. coli lac repressor genes.

Amino Acid Sequence↗
PubMed1985

Regulatory region of the divergent Klebsiella pneumoniae lac operon.

The chromosomal DNA that lies between the lacI and lacZ genes of Klebsiella pneumoniae constitutes a 196-base pair intercistronic region that contains regulatory sequences for both genes. The probable locations of specific regulatory elements for both lacI and lacZ genes were determined by analogy with the corresponding Escherichia coli sequences. A recombinational event in ancestral DNA evidently has inverted the transcriptional direction of lacI in K. pneumoniae relative to the transcriptional direction of lacI in E. coli. One end of the inversion was located within a 19-base pair sequence in the K. pneumoniae regulatory region. Sequences partially homologous to these 19 base pairs were found in two locations on either side of the E. coli lacI gene. The nucleotide sequence of the lac regulatory region in K. pneumoniae exhibits more than one possibility for folded tertiary structures. The spatial relationships of transcriptional binding sites differ in two possible structures. Associations of regulatory and transcriptional proteins with the DNA might affect conformation of the regulatory sequences and, as a consequence, transcription of the lac genes.

Base Sequence↗
PubMed1985

Pump and leak in regulation of fluid transport in rabbit cornea.

Rabbit corneas were isolated, denuded of epithelium, and perfused on the anterior and posterior surfaces with Krebs Ringer-bicarbonate with additions of 50 microM H2O2, 125 microM BCNU, or 100 microM ouabain. The permeability of the corneal endothelium to labelled mannitol and inulin was determined by adding these compounds to the endothelial perfusate and measuring the rate of appearance of radioactivity in the anterior perfusate. Both H2O2 and BCNU increased the flux of mannitol and inulin across the endothelium in a time dependent manner, but ouabain had no effect. Additions of glucose with H2O2 or of GSH with BCNU prevented the observed changes in permeability. ATPase activities in the endothelia of intact, isolated corneas were also determined following incubation in the same media. The only observable effects of H2O2 and BCNU were slight reductions in the activity of Na+ + K+ ATPase. It is concluded that permeability changes, the leak, are more critical than active transport processes, the pump, in determining the rate and extent of swelling that results from exposure of the cornea to these agents.

Adenosine Triphosphatases↗
PubMed1984

Physical map of Salmonella typhimurium LT2 DNA in the vicinity of the proA gene.

More than 55 kilobases of chromosomal DNA of Salmonella typhimurium LT2, including the gpt, proA, ataA, and newD genes, were cloned in plasmid vector pULB113. The locations of the genes and selected restriction endonuclease cleavage sites were established, and some of the restriction enzyme fragments were subcloned in plasmid vector pBR322.

Bacterial Proteins↗
PubMed1984

Location and analysis of nucleotide sequences at one end of a putative lac transposon in the Escherichia coli chromosome.

A segment of Escherichia coli DNA that contained a discontinuity of homology with Salmonella typhimurium DNA was isolated. The segment, 1,430 base pairs long, was derived from one end of the lac "loop," a region of about 12 kilobase pairs of E. coli DNA, including the lac operon which has no detectable homology with S. typhimurium DNA (K. Lampel and M. Riley, Mol. Gen. Genet. 186:82-86, 1982). The nucleotide sequence of the 1,430-base-pair segment of DNA was determined. The location of the junction of discontinuity of homology within the segment was established by hybridization experiments. Nucleotide sequences at or near the junction were determined to be similar to sequences that are involved in site-specific inversion in S. typhimurium, E. coli, phage P1, and phage Mu. Similar sequences are also present within the terminal inverted repeat sequences of transposon Tn5 and at the V-D-J joining sequences of eucaryotic immunoglobulin genes. Therefore, the lac operon, together with flanking DNA, may have been inserted into the E. coli chromosome at one time via a site-specific recombination event. Rearrangement events of this kind undoubtedly have played a significant role in the evolutionary divergence of chromosomal DNAs.

Base Composition↗
PubMed1983

Diazepam increases GABA mediated inhibition in the olfactory cortex slice.

The effect of diazepam on inhibition has been examined using an in vitro preparation of the guinea-pig olfactory cortex. Diazepam (0.03-30 mumol/l) doubled the intensity and duration of the recurrent inhibitory conductance. Diazepam had no effect on single evoked excitatory post-synaptic potential (e.p.s.p.) nor any effects on the action potential or membrane electrical constants. Diazepam (0.003-100 mumol/l) also reduced the multisynaptic e.p.s.p. generated through a recurrent pathway directed at the soma when elicited during the time-course of the inhibitory conductance. Diazepam had a comparitively small effect on the monosynaptic e.p.s.p. generated on the distal dendrite. Pentobarbitone had a similar though more intense effect over a narrow concentration range (10-200 mumol/l). The inhibitory coductance is thought to be GABA-mediated. Diazepam doubled the potency of the GABA analogue, muscimol, when applied via the bathing solution, whereas a modest 50 mumol/l pentobarbitone increased muscimol potency by about four-fold. The mild but selective effect of diazepam contrasts with the more intense and general effects of pentobarbitone and supports the idea that these drugs act through different mechanisms at the GABA receptor/channel complex.

Animals↗
PubMed1983

Cloning the Escherichia coli K-12 argD gene specifying acetylornithine delta-transaminase.

The argD gene of Escherichia coli was shown to be present in plasmids pLC2-28 and pLC3-11 of the collection of Clarke and Carbon [Cell 9 (1976) 91-99]. The gene was cloned into pBR322 as a 6.3-kb BamHI fragment. Enzyme determination showed that the cloned DNA contains the structural gene for acetylornithine delta-transaminase. The argD DNA was used as a probe in hybridization experiments which indicated that the argM gene resides in a duplicated portion of E. coli DNA that is highly similar to the argD region.

Arginine↗
PubMed1983

Cloning chromosomal lac genes of Klebsiella pneumoniae.

The chromosomal gene for beta-galactosidase from Klebsiella pneumoniae strain T17R1 and associated regulatory genes have been cloned as a 5-kb HindIII fragment in the pBR322 plasmid vector. The beta-galactoside permease gene is not present in a functional form in the 5-kb fragment. The K. pneumoniae genes are expressed in an Escherichia coli host. The synthesis of beta-galactosidase is inducible by isopropyl-beta-D-galactosidase (IPTG) and is sensitive to catabolite repression. There appears to be greater homology between the K. pneumoniae and E. coli structural genes for beta-galactosidase than there is between the respective repressor genes.

Cloning, Molecular↗
PubMed1983

Identification of the polypeptides encoded in the ATPase 6 gene and in the unassigned reading frames 1 and 3 of human mtDNA.

Antibodies prepared against chemically synthesized peptides predicted from the DNA sequence have been used to identify the polypeptides encoded in the ATPase 6 gene and in unidentified reading frames (URFs) 1 and 3 of human mtDNA. In particular, antibodies directed against the COOH-terminal nonapeptide of the putative polypeptide encoded in the ATPase 6 reading frame immunoprecipitated specifically component 17 of the HeLa cell mitochondrial translation products, the reaction being inhibited by the specific peptide. Similarly, antibodies directed against the COOH-terminal undecapeptide of the putative URF1 product or against the COOH-terminal heptapeptide of the presumptive URF3 product were effective in immunoprecipitating specifically component 12 or, respectively, component 24 of the mitochondrial translation products. The sizes of proteins 17, 12, and 24, as estimated from their electrophoretic mobilities, are compatible with their being the products of the ATPase 6 gene, URF1, and URF3, respectively.

Adenosine Triphosphatases↗
PubMed1983

Employee performance reviews that work.

Employee performance reviews can often be a frustrating, time-consuming and unproductive process for both the employee and the manager. This article outlines three steps that will make an employee performance review system more effective. According to the author, EPRs can be used to increase productivity, improve morale, and create better communication.

Employee Performance Appraisal↗
PubMed1982

Discontinuity of homology of Escherichia coli and Salmonella typhimurium DNA in the lac region.

Partial homology of Salmonella typhimurium DNA to Escherichia coli DNA was demonstrated by Southern hybridization blots to exist on either side of the lac operon of E. coli but no homology was detected between S. typhimurium DNA and about 12 kb of E. coli DNA including the lac genes as well as about 5 kb of E. coli DNA between lac and proC. Thus portions of DNA seem to have been either added to the E.coli genome or deleted from the S. typhimurium genome since their divergence from a common ancestor. Although an IS1 element was located near the lac operon of E. coli, the insertional element was shown not to be near any of the junctures of discontinuity of E. coli--S. typhimurium homology near lac.

Base Sequence↗
PubMed1980

Conserved genes in enteric bacteria are not identical.

In addition to ribosomal RNA genes, a relatively small number of genes are highly conserved between Escherichia coli and Salmonella typhimurium on the one hand, and either Serratia marcescens or Proteus morganii on the other hand. The conserved non-rRNA genes are not the same in S. marcescens and P. Morganii. Different genetic segments have maintained nucleotide sequence similarity to parts of the E. coli and S. typhimurium genomes in the course of the evolution of S. marcescens and P. morganii.

Base Sequence↗
PubMed1980

Conservation and variation of nucleotide sequences within related bacterial genomes: Escherichia coli strains.

Changes in the patterns produced by annealing restriction endonuclease digests of bacterial genomes with probe deoxyribonucleic acids (DNAs) containing small portions of a bacterial genome provide sensitive indicator of the degree of nucleotide sequence relatedness that exists in localized regions of the genomes of closely related bacteria. We have used five probe DNAs to explore the relatedness of parts of the genomes of six laboratory Escherichi coli strains. A range in in the amount of variability in the positions of restriction enzyme cleavage sites in the selected portions of the genomes was found. Portions of the genome that are believed to be inacative were more variable than portions that contained functional genes: the sites in and near regions of homology to phage lambda DNA in the genome showed the greatest variability. These regions probably represent remnants of cryptic prophages. Variability was assessed pairwise among four of the E. coli strains and ranged from 5 to > 25% base pair substitutions in the lambda-related regions. In contrast, the endonuclease cleavage sites in the trp, tna, lac, thy regions, and one other as-yet-unidentified segment of the genome were more highly conserved. It seems likely that these sites lie in genetic locations that are subject to functional constraints.

Bacteriophage lambda↗
PubMed1980

Conservation and variation of nucleotide sequences within related bacterial genomes: enterobacteria.

We have assessed the degree of relatedness of several portions of the Escherichia coli genome to the corresponding portions of the genomes of representative enteric bacteria, using the Southern transfer and hybridization technique (E. Southern, J. Mol. Biol. 98:503-517, 1975). The degree of relatedness varied among the regions examined. Judging both by the relative amounts of deoxyribonucleic acid in the various enteric genomes that are highly homologous and by the conservation of positions of restriction enzyme cleavage sites in these regions, the enteric genomes have diverged to greater extents in some parts of the genomes than in others. Portions of the genomes (including the tnaA and thyA genes, the trp operon, and one other unassigned segment) appear to have evolved in concert with the genome as a whole. By contrast, the lacZ gene and portions of the genome that are homologous to phage lambda vary more widely, perhaps reflecting a separate evolutionary origin for these segments of deoxyribonucleic acid.

Bacteriophage lambda↗
PubMed1980

Conservation and variation of nucleotide sequences in Escherichia coli strains isolated from nature.

A group of Escherichia coli isolates from nature were compared with one another and with laboratory strains of E. coli with respect to size distribution of chromosomal restriction endonuclease fragments and differences in nucleotide sequences in selected small portions of the genomes. The estimated frequency of base substitutions in nucleotide sequences in and near the trp operons of 26 of the 28 E. coli strains examined ranged from 0.008 to 0.066. Nucleotide sequences in or near lambda prophage homologs were significantly more variable than the sequences in or near trp, tnaA, and thyA genes. Thus, the lambda-homologous regions may have a significant horizontal component in their evolutionary histories, having undergone genetic exchange, whereas the trp, tnaA, and thyA regions may have solely vertical evolutionary histories. The relatedness of the E. coli strains in the genetic regions studied indicated that laboratory strains are not more closely related to one other than they are to isolates from nature. The isolates from natural populations did not form groups related either by host taxa or by geographical region of isolation.

Bacteriophage lambda↗
PubMed1979

The amino acid sequence of the alpha-chain of human fibrinogen.

The amino acid sequence of the human fibrinogen alpha-chain reveals a structure that can be divided into three zones of unique amino acid composition. The middle of these contains the two primary alpha-chain cross-linking acceptor sites and consists of a remarkable series of internal duplications.

Amino Acid Sequence↗