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L M Hall

Publications and source records attributed to L M Hall.

At least 91 records · Page 5Linked to original sources
PubMed1993

Molecular characterization of a conserved, guanine nucleotide-dependent ADP-ribosylation factor in Drosophila melanogaster.

ADP-Ribosylation factors (ARFs) are ubiquitous approximately 20-kDa guanine nucleotide-binding proteins that stimulate cholera toxin-catalyzed ADP-ribosylation in vitro. Because the functional role(s) of ARF in mammalian systems is (are) elusive, we looked for ARF in Drosophila melanogaster, and report the partial purification and molecular cloning of an ARF from Drosophila. We cloned the Drosophila ARF 1 gene without library screening by a combination of 5 polymerase chain reactions (PCRs), yielding a 546-base open reading frame encoding 182 amino acids, which are > 93% identical to those of mammalian class I ARFs. This ARF gene maps to 79F3-6 in the proximal region of the left arm of Drosophila chromosome 3. The Drosophila ARF1 gene structure, including placement of introns, is highly conserved relative to mammalian class 1 ARF genes. A single ARF mRNA species of 1.8 kb was abundant in all Drosophila body segments. Recombinant Drosophila ARF 1 synthesized in Escherichia coli had biochemical and immunochemical activities similar to those of mammalian ARF. The similarities of sequence and biochemical properties between Drosophila and mammalian ARFs contrast with their differences from Drosophila arl (ARF-like protein), which does not stimulate cholera toxin-catalyzed ADP-ribosylation, and is only approximately 52-56% identical in amino acid sequence to mammalian ARFs.

ADP-Ribosylation Factor 1↗
PubMed1993

Expression of a foreign gene in Chlamydomonas reinhardtii.

Genomic transformation of Chlamydomonas reinhardtii exposed to glass-bead abrasion was accomplished with a chimeric neomycin phosphotransferaseII (NPTII)-encoding gene (nos::npt) flanked by the nopaline synthase promoter and polyadenylation sequences obtained from the Ti plasmid of Agrobacterium tumefaciens. These sequences were in a plasmid (pGA482) which also contained gene nit1 encoding nitrate reductase of C. reinhardtii. Transformants were selected by their ability to grow on medium containing nitrate, and 52% of these was also resistant to kanamycin. Evidence for nos::npt expression includes: (1) hybridization with probes specific for npt, (2) demonstration of NPTII activity after electrophoresis of extracts, and (3) chromatographic identification of the reaction product of NPTII, kanamycin phosphate. The highly biased codon usage in Chlamydomonas does not preclude expression.

Agrobacterium tumefaciens↗
PubMed1993

Muscarinic acetylcholine receptors in invertebrates: comparisons with homologous receptors from vertebrates.

The pharmacology, physiology and molecular biology of invertebrate muscarinic acetylcholine receptors are compared with current knowledge concerning vertebrate muscarinic acetylcholine receptors. Evidence for the existence of multiple receptor subtypes in invertebrates is examined, emphasizing what is presently known about the sensitivity of invertebrate preparations to subtype selective ligands previously defined in vertebrate studies. Other evidence for muscarinic receptor subtypes which is examined includes: heterogeneous responses to classical muscarinic ligands and evidence for coupling of invertebrate muscarinic receptors to several different classes of second messenger systems. Clues regarding possible functions for invertebrate muscarinic receptors are discussed, including evidence from both physiological studies and in situ localization studies which reveal patterns of receptor protein and mRNA expression. A detailed analysis of the structural similarities between a cloned Drosophila muscarinic receptor and vertebrate muscarinic receptors is also presented. Regions of the receptors that may be involved in ligand binding, effector coupling and receptor regulation are identified in this comparison. Future directions for invertebrate muscarinic receptor research are considered including: methods for cloning other receptor subtypes, methods for cloning homologous receptors from other species and genetic approaches for determining the physiological roles of muscarinic receptors.

Amino Acid Sequence↗
PubMed1993

The relationship between yolk cholesterol and total lipid concentration throughout the first year of egg production in the domestic fowl.

1. Variation of egg yolk cholesterol and total lipid concentration (mg/g wet yolk) throughout the first year of egg production for the domestic fowl is described. 2. Yolk cholesterol concentration decreases between 20 and 30 weeks of age, and then remains constant until 70 weeks of age. Yolk total lipid concentration increases to a maximum at 40 weeks of age before decreasing to its original value at 60 and 70 weeks of age. 3. Bird means for yolk cholesterol and total lipid concentration are negatively related at 20 weeks of age, and essentially independent for the remainder of the first year of egg production. 4. Variation for yolk cholesterol concentration between 30 and 70 weeks of age appears to be a consequence of differences in the proportion of cholesterol to other lipid components. 5. Uptake of plasma lipoproteins characteristic of the immature bird is likely to be responsible for the high yolk cholesterol concentration at 20 weeks of age.

Age Factors↗
PubMed1993

OXA-11, an extended-spectrum variant of OXA-10 (PSE-2) beta-lactamase from Pseudomonas aeruginosa.

Pseudomonas aeruginosa ABD, which was isolated in October 1991 from blood cultures of a burn patient in Turkey, was resistant to cephalosporins, particularly ceftazidime (MIC, 512 micrograms/ml), penicillins, aztreonam, and meropenem, but not to imipenem. Cephalosporin and penicillin resistance transferred to P. aeruginosa PU21 and was associated with a beta-lactamase with a pI of 6.4 encoded by a 100-MDa plasmid designated pMLH52. Like extended-spectrum TEM and SHV beta-lactamases, this enzyme hydrolyzed penicillins and newer cephalosporins but did not hydrolyze cefoxitin or carbapenems. However, it differed from TEM and SHV derivatives in being a potent oxacillinase, and its encoding gene did not hybridize with probes to TEM and SHV genes. To characterize the enzyme, libraries of total DNA were cloned into plasmid pUC19 and were transformed into Escherichia coli DH5 alpha. Recombinant plasmids that gave ceftazidime resistance all contained a 3.65-kb BamHI fragment. Deletions from this fragment allowed the beta-lactamase gene to be located on a 1.4-kb section of DNA, which contained an open reading frame of 798 bases. This encoded a protein that was deduced to differ from PSE-2 beta-lactamase only in having serine instead of asparagine at position 143 and aspartate instead of glycine at position 157. It is concluded that the resistance of isolate ABD dependent on an extended-spectrum variant of the PSE-2 enzyme. The ability of this enzyme to cause ceftazidime resistance dependent primarily on a low Km for the compound; Vmax remained low. It is proposed that PSE-2 should be transferred to the OXA group as OXA-10 and that the new enzyme be designated OXA-11.

Amino Acid Sequence↗
PubMed1992

Platelet dense granule release reaction monitored by high-performance liquid chromatography-fluorometric determination of endogenous serotonin.

The platelet dense granule release reaction was monitored by measuring the serotonin content of platelets collected by filtration following release. Sensitive HPLC-fluorometric analysis permitted release to be assessed using small (25-50 microliters) volumes of plasma and whole blood. Release could be examined for periods as short as 1 s due to the rapid stoppage effected by filtration. The half-life of thrombin-stimulated (1 U/ml) release was 2-3 s, the EC50 values observed for thrombin-stimulated release over a 60-s release period were 0.01-0.03 U/ml for diluted whole blood and plasma samples.

Blood Platelets↗
PubMed1992

Variation in egg yolk cholesterol concentration between and within breeds of the domestic fowl.

1. The pattern of variation for egg yolk cholesterol concentration between 5 commercial egg layer lines and a cross of Gallus domesticus is described. 2. Yolk cholesterol concentration in the cross was lower than in the lines, and 6.7% lower than the midparent value. 3. It is proposed that the reduced yolk cholesterol concentration of the cross may be a consequence of heterosis, although sex-linkage and/or maternal effects cannot be discounted. 4. The difference between the cross and parental lines is consistent with a physiological relationship between yolk cholesterol concentration and rate of egg production, but not between yolk cholesterol concentration and yolk weight.

Animals↗
PubMed1992

Survey of the prevalence of beta-lactamases amongst 1000 gram-negative bacilli isolated consecutively at the Royal London Hospital.

beta-Lactamase expression was examined in 1000 consecutive Gram-negative bacilli isolated from urine, wound swab, sputum or blood specimens received at the Microbiology Laboratory of the Royal London Hospital. This survey, performed between January and April, 1991, followed a similar study undertaken in early 1982. The distribution of species was similar in the two surveys, except that the proportion of Pseudomonas aeruginosa isolates had increased from 11% in 1982 to 17.5% in the present study. This increase was balanced by a decreased proportion of enterobacteria. Amongst plasmid-mediated beta-lactamases, TEM-1 (especially), TEM-2, SHV-1 and OXA types continued to predominate in enterobacteria. Their frequency in Escherichia coli was unchanged (46% in 1991 compared with 43% in 1982), but had increased from 5 to 22% amongst Proteus mirabilis isolates. An apparent decrease in their frequency amongst Enterobacter cloacae isolates, from 48% in 1982 to 17% in 1991, probably reflected changes to strain prevalence rather than enzyme prevalence. Plasmid type beta-lactamases were present in fewer than 2% of P. aeruginosa isolates in both surveys. In the present study, chromosomal beta-lactamase derepression (constitutive hyperproduction) was detected in 10/76 isolates of E. cloacae, Enterobacter aerogenes, Citrobacter freundii, Serratia spp. and Morganella morganii, and in 2/170 P. aeruginosa isolates. These proportions were increased, compared with those seen the 1982 survey, though the significance was borderline (P approximately 0.05; chi 2 test). Extended-spectrum plasmid mediated beta-lactamases, unknown in 1982, were found in 11/70 Klebsiellae pneumoniae isolates in the present study. Ten of these organisms, representing at least five distinct strains, produced TEM-10 enzyme, encoded by a plasmid of c. 90 kb; the remaining organism had an unidentified SHV-derived enzyme.

Anti-Bacterial Agents↗
PubMed1992

Typing of Enterococcus species by DNA restriction fragment analysis.

Enterococci are a frequent cause of hospital-acquired infection, being associated with urinary tract infections, wound sepsis, bacteremia, and endocarditis. The source of infection is usually thought to be endogenous, but some evidence points to cross-infection between patients. A better understanding of the epidemiology of enterococci has been limited by the lack of a good discriminatory typing system. This report describes the application of two DNA-based typing methods to Enterococcus faecalis and Enterococcus faecium: comparison of restriction fragments from total DNA by conventional electrophoresis and comparison of restriction fragments hybridizing to an rRNA gene probe (ribotyping). Comparison of restriction fragments (from SstI digestion) by conventional electrophoresis was simple and highly discriminatory. The results of analysis of blood culture isolates and of repeat isolates from individual patients are reported. Ribotyping (with BscI digestion) was more applicable at the level of species discrimination.

Bacteremia↗
PubMed1992

Epidemiology of Enterococcus faecalis urinary tract infection in a teaching hospital in London, United Kingdom.

Enterococcus faecalis is a frequent cause of urinary tract infection in hospitalized patients. Recent reports have suggested that the organism may frequently be acquired by cross-infection from other patients. In this study, we used total DNA restriction patterns to type 135 urine isolates of E. faecalis from four sets of patients. Isolates were placed into types (all bands identical) and into groups (most bands identical). Most isolates were discriminated by the typing method, and the results suggested that direct cross-infection occurred rarely if at all. However, two groups of clonally related isolates occurred frequently in the urine specimens and also in feces from hospital-associated patients and were often associated with antibiotic resistance. Isolates from these two groups were found less frequently in feces from people not associated with the hospital.

Cluster Analysis↗
PubMed1991

The acetylcholinesterase gene of Anopheles stephensi.

1. The acetylcholinesterase (AChE) gene from the important malaria vector Anopheles stephensi has been isolated by homology to the Drosophila acetylcholinesterase gene. 2. The complete sequence and intron-exon organization has been determined. The encoded protein has 69% identity to Drosophila AChE and 38 and 36% identity to Torpedo AChE and human butyrylcholinesterase, respectively.

Acetylcholinesterase↗
PubMed1991

Activity of clavulanate combinations against TEM-1 beta-lactamase-producing Escherichia coli isolates obtained in 1982 and 1989.

Recent reports of decreased susceptibility to amoxycillin/clavulanate and ticarcillin/clavulanate combinations amongst Escherichia coli isolates have been attributed to an increased frequency of hyperproduction of TEM-1 beta-lactamase. To test this claim we compared the activities of clavulanate combinations against consecutive E. coli isolates producing TEM-1 beta-lactamase that were obtained from clinical material at The London Hospital during 1982 (n = 50) and 1989 (n = 46). Enzyme production was quantified and related to the level of clavulanate required to potentiate amoxycillin and ticarcillin. The levels of TEM-1 enzyme production varied 150-fold amongst the isolates, partly because of variation in the gene copy number. A clear correlation existed between enzyme quantity and levels of resistance to the clavulanate combinations. However, there was no significant difference (P greater than 0.05, Mann-Whitney U test) between the isolates obtained in 1982 and 1989 in terms of the clavulanate concentrations required to potentiate the penicillins, or in the distribution of beta-lactamase activities present.

Amoxicillin↗
PubMed1990

Cloning, localization, and permanent expression of a Drosophila octopamine receptor.

A cDNA for a member of the G protein-coupled receptor family was isolated from Drosophila using a probe derived from a human beta 2-adrenergic receptor cDNA. This Drosophila receptor gene is localized at 99A10-B1 on the right arm of chromosome 3 and is preferentially expressed in Drosophila heads. The insect octopamine receptor has been permanently expressed in mammalian cells, where it mediates the attenuation of adenylate cyclase activity and exhibits a pharmacological profile consistent with an octopamine type 1 receptor. Sequence and pharmacological comparisons indicate that the octopamine receptor is unique but closely related to mammalian adrenergic receptors, perhaps as an evolutionary precursor.

Amino Acid Sequence↗
PubMed1990

Cross-Resistance of a Chlorsulfuron-Resistant Biotype of Stellaria media to a Triazolopyrimidine Herbicide.

A biotype of Stellaria media (L.) Vill. has been identified that is highly resistant to the herbicide chlorsulfuron. Resistance is due to an altered acetolactate synthase (ALS) that is much less sensitive to chlorsulfuron than the ALS from the susceptible (S) biotype. The S biotype was extremely sensitive to D489 (N-[2,6-dichlorophenyl]-5,7-dimethyl-1,2,4-triazolo[1,5a] pyrimidine-2-sulfonamide), a member of a new class of triazolopyrimidine herbicides, while the chlorsulfuron-resistant biotype exhibited complete cross-resistance at both the whole plant and enzyme levels. ALS activity of the S biotype was reduced by approximately 90% in the presence of 0.1 micromolar D489, while that of the R biotype was reduced by less than 10%. This result suggests that the two herbicides share a common binding site on ALS. Only very slight cross-resistance at the ALS level was found to imazamethabenz, an imidazolinone herbicide.

Journal Article↗
PubMed1990

Characterization of two classes of opioid binding sites in Drosophila melanogaster head membranes.

Opioid receptors have been characterized in Drosophila neural tissue. [3H]Etorphine (universal opioid ligand) bound stereospecifically, saturably, and with high affinity (KD = 8.8 +/- 1.7 nM; Bmax = 2.3 +/- 0.2 pmol/mg of protein) to Drosophila head membranes. Binding analyses with more specific ligands showed the presence of two distinct opioid sites in this tissue. One site was labeled by [3H]dihydromorphine ([3H]DHM), a mu-selective ligand: KD = 150 +/- 34 nM; Bmax = 3.0 +/- 0.6 pmol/mg of protein. Trypsin or heat treatment (100 degrees C for 15 min) of the Drosophila extract reduced specific [3H]DHM binding by greater than 80%. The rank order of potency of drugs at this site was levorphanol greater than DHM greater than normorphine greater than naloxone much greater than dextrorphan; the mu-specific peptide [D-Ala2,Gly-ol5]-enkephalin and delta-, kappa-, and sigma-ligands were inactive at this site. The other site was labeled by (-)-[3H]ethylketocyclazocine ((-)-[3H]EKC), a kappa-opioid, which bound stereospecifically, saturably, and with relatively high affinity to an apparent single class of receptors (KD = 212 +/- 25 nM; Bmax = 1.9 +/- 0.2 pmol/mg of protein). (-)-[3H]EKC binding could be displaced by kappa-opioids but not by mu-, delta-, or sigma-opioids or by the kappa-peptide dynorphin. Specific binding constituted approximately 70% of total binding at 1 nM and approximately 50% at 800 nM for all three radioligands ([3H]etorphine, [3H]EKC, and [3H]DHM). Specific binding of the delta-ligands [3H][D-Ala2,D-Leu5]-enkephalin and [3H][D-Pen2,D-Pen5]-enkephalin was undetectable in this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Drosophila melanogaster acetylcholinesterase gene. Structure, evolution and mutations.

Acetylcholinesterase is a key component of cholinergic neurotransmission. In Drosophila melanogaster, acetylcholinesterase is encoded by the Ace locus. We have determined the complete organization of the locus. The transcription unit is 34 kb (1 kb = 10(3) bases) long and encompasses ten exons. We have mapped the 5' end of the transcript, sequenced all the intron/exon boundaries, as well as the 3' end of the transcript. The deduced mature transcript is 4291 nucleotides long without poly(A). Sequencing of the promoter region reveals a potential TATA box and (GA)n motives. The Drosophila coding sequence is more split than its vertebrate counterparts, but the splicing sites of the two last exons are precisely conserved among Drosophila and vertebrate cholinesterases, and intriguingly also with the bovine thyroglobulin gene. Finally, a number of the mutations isolated in earlier genetic work are precisely placed on our molecular map in introns, exons and promoter regions. Among them, for example, a short deletion known to affect acetylcholinesterase level and tissue distribution removes promoter regions and the first non-coding exon.

Acetylcholinesterase↗