Search PubMed⌕ Search

Biomedical subjects

A J Clark

Publications and source records attributed to A J Clark.

At least 271 records · Page 15Linked to original sources
PubMed1985

Elevated epidermal growth factor receptor gene copy number and expression in a squamous carcinoma cell line.

The human epidermal growth factor (EGF) receptor is known to be homologous to the v-erb B oncogene protein of the avian erythroblastosis virus. Overexpression of the EGF receptor gene in A431 epidermoid carcinoma cells is due to gene amplification. In this study, a variety of squamous cell carcinomas were examined and one, SCC-15, contained high levels of the EGF receptor as determined by immunoprecipitation via an EGF receptor-specific polyclonal antibody. Using a cloned EGF receptor complementary DNA as a probe, the level of EGF receptor RNA was found to be elevated four-fold in SCC-15 relative to normal cultured keratinocytes. When the same probe was used to identify EGF receptor gene fragments on a genomic DNA blot, the SCC-15 cell line was shown to possess an EGF receptor gene copy number amplified four to five times. Gene amplification results in the enhancement in the level of the EGF receptor in several carcinomas and could be responsible for the appearance of the transformed phenotype in these cells.

Carcinoma, Squamous Cell↗
PubMed1985

Vitamin B-6 status of southern adolescent girls.

The vitamin B-6 status of 583 white and black adolescent girls living in Alabama, Arkansas, North Carolina, Oklahoma, and Virginia was assessed using the parameters coenzyme stimulation of erythrocyte alanine aminotransferase activities and dietary intakes of the vitamin. The sample included 382 white and 201 black girls who were 12, 14, or 16 years of age; the sample was also divided into low, medium, and high per capita income groups. The height and weight measurements of the subjects were within normal ranges. The mean estimated daily vitamin B-6 intake of the girls from food sources was 1.20 mg daily, as indicated by evaluation of data obtained via two nonsequential 24-hour food recalls; about half of the subjects reported consuming less than 66% of the Recommended Dietary Allowance for the vitamin. Approximately 20% of the girls had marginal vitamin B-6 status and 13%, deficient status, as indicated by coenzyme stimulation values. Coenzyme stimulation and dietary values of the race, age, and income groups were similar. Vitamin B-6 inadequacy appears to be fairly prevalent among white and black southern adolescent girls.

Adolescent↗
PubMed1984

Changes in membrane ionic conductance, but not changes in slip, can account for the non-linear dependence of the electrochemical proton gradient upon the electron-transport rate in chromatophores.

Decrease in the rate of cyclic electron transport (JE) measured from the absorbance changes associated with reaction centre bacteriochlorophyll led to a less than proportionate decrease in the membrane potential (delta psi) measured by electrochromism. In principle this result can be explained either by a delta psi-dependent slip in the H+/e- coupling ratio (nE) or by a delta psi-dependent change in the membrane ionic conductance. Simultaneous measurement of the membrane ionic current (JDIS) did not reveal any significant changes in the H+/e- ratio (JDIS/JE) and showed that conductance changes (JDIS/delta psi) account quantitatively for the curved dependence of delta psi on JE. Simultaneous recordings of JDIS and the extravesicular pH from cresol-red absorbance changes, suggest that protons are the main current-carrying species across the chromatophore membrane at high values of delta psi in the presence and absence of Fo-ATPase inhibitor. At reduced delta psi the flux of other ions outweighs the hydrogen ion current.

Absorption↗
PubMed1984

Amplification and enhanced expression of the epidermal growth factor receptor gene in A431 human carcinoma cells.

The sequence of the human epidermal growth factor (EGF) receptor shows great homology with the avian erythroblastosis virus v-erb B oncogene, raising the possibility that the receptor gene is identical to the c-erb B protooncogene. Human A431 epidermoid carcinoma cells, which have an unusually high number of EGF receptors, were examined to determine whether elevated EGF receptor levels correlate with gene amplification. Southern blots of genomic DNA's from A431 and other human cell lines were probed with either a v-erb B gene fragment or a human EGF receptor complementary DNA clone (pE7), previously isolated from an A431 complementary DNA library. When either probe was used to analyze Eco RI- or Hind III-generated DNA fragments, EGF receptor DNA sequences were amplified about 30-fold in A431. Differences in the banding pattern of A431 DNA fragments relative to normal fibroblast DNA indicate the occurrence of a rearrangement in the region of the receptor gene. Furthermore, A431 cells contain a characteristic, prominent 2.9-kilobase RNA. These results are consistent with the hypothesis that, in A431 cells, gene amplification, possibly associated with a translocation event, may result in the overproduction of EGF receptor protein or the appearance of the transformed phenotype (or both).

Alpharetrovirus↗
PubMed1984

Structure of mouse major urinary protein genes: different splicing configurations in the 3'-non-coding region.

The multigene family which codes for the mouse major urinary proteins (MUPs) consists of approximately 35 genes. Most of these are members of two different groups, Group 1 and Group 2, which can be distinguished by nucleic acid hybridisation. Here we describe the structure of a Group 1 gene and show that two size classes of MUP mRNA which are found in mouse liver result from different splicing events in the 3'-non-coding region and contain different polyadenylation sites. Short mRNA is approximately 750 nucleotides long, contains six exons, and is the main product of the Group 2 genes. Long mRNA is approximately 880 nucleotides long, contains seven exons and is the main product of the Group 1 genes. Five exons and part of the sixth are common to long and short mRNA and contain the coding region. This codes for an acidic protein of 180 amino acids containing an 18 residue signal peptide. A comparison of the mouse sequence with a homologous rat alpha 2u-globulin sequence shows that the rate of evolutionary divergence of the two proteins has been high. Silent sites have diverged four times more rapidly than replacement sites, showing that there has been selection against change in the protein sequence.

Amino Acid Sequence↗
PubMed1984

A 45-kb DNA domain with two divergently orientated genes is the unit of organisation of the murine major urinary protein genes.

The multigene family which codes for the mouse major urinary proteins (MUPs) consists of approximately 35 genes. Most of these are members of two different groups, Group 1 and Group 2, which can be distinguished by nucleic acid hybridisation. By screening a Charon 4A library of mouse DNA with probes from the 5'-flanking region of a MUP gene, we have isolated clones that contain both a Group 1 and a Group 2 gene, orientated in a divergent fashion, with 15 kb of DNA between the 5' ends of the genes. We show that this pairwise arrangement is the predominant organisation of MUP genes in the BALB/c genome. We argue that the head-to-head gene pair is the unit both of DNA organisation and of evolution. Taking into account the genes themselves, the intervening 15 kb and the homologous 3'-flanking regions, this unit is approximately 45 kb long. We also show that some MUP genes may be linked in a tail-to-tail fashion with 26-28 kb between the 3' ends of two genes. This suggests that the minimum distance between successive 45-kb units is approximately 7 kb.

Animals↗
PubMed1984

Molecular analysis of the recF gene of Escherichia coli.

We analyzed the nucleotide sequence of a 1.325-kilobase region of wild-type Escherichia coli containing a functional recF gene and six Tn3 mutations that inactivate recF. The analysis shows a potentially translatable reading frame of 1071 nucleotides, which is interrupted by all six insertions. A protein of 40.5 kilodaltons would result from translation of the open reading frame, and a radioactive band of protein of an apparent molecular weight of approximately 40 kilodaltons was seen by the maxicell method using a recF+ plasmid. Putative truncated peptides were seen when two recF::Tn3 mutant plasmids were used. Differential expression of dnaN and recF from a common promoter was noted. recF332::Tn3 was transferred to the chromosome where, in hemizygous condition, it produced UV sensitivity indistinguishable from that produced by two presumed recF point mutations.

Amino Acid Sequence↗
PubMed1984

Genetic analysis of the recJ gene of Escherichia coli K-12.

An insertion of transposon Tn10 was isolated in a gene essential for the RecF pathway of recombination. This mutation and six other previously isolated rec mutations, including one in the recJ gene, were mapped to 62 min on the Escherichia coli chromosome. All seven mutations were examined for their effects on recombination and UV survival in several genetic backgrounds. Although all affected the RecF, and not the RecBC, pathway of recombination, they could be separated into two classes: four severely reduced UV survival and three did not. In addition, whereas the effects of the former class appeared to be nearly equivalent in recB recC sbcA and recB recC sbcB mutant backgrounds, the latter class affected recombination differentially. The latter class was found to be either "leaky" or temperature-sensitive mutations. Transductional complementation assays indicated that representative members of each class were mutations in the same gene, recJ. Possible explanations for the differences in phenotypic effects produced by these recJ mutations are discussed.

Chromosome Mapping↗
PubMed1984

Two-component suppression of recF143 by recA441 in Escherichia coli K-12.

Sensitivity to UV irradiation conferred by recF143 was partially suppressed by recA441 (also known as tif-1). A temperature-conditional component depended on uvrA function and is thought to involve thermal induction of excision repair enzymes. In a uvrA6 mutant, a temperature-independent component of suppression was seen. This is thought to indicate that recA441 also caused temperature-independent changes in recA activity. Two hypotheses are offered to explain how recA441 produced both thermosensitive and thermoindependent effects.

Bacterial Proteins↗
PubMed1983

The influence of the ionic conductance on the relation between electron transport and proton-motive force in intact cells of Rhodopseudomonas capsulata.

1. The dependence of membrane potential (delta psi) on the rate of respiration in darkened intact cell suspensions of Rhodopseudomonas capsulata was distinctly non-linear: severe inhibition of respiration with either rotenone or KCN led to only a small drop in delta psi. 2. In the presence of 0.3 microMs carbonylcyanide p-trifluoromethoxyphenylhydrazone [CF3OPhzC(CN)2] the dependence of delta psi on respiratory rate became linear. Consequently, and particularly at lower concentrations of CF3OPhzC(CN)2, there was a pronounced, synergistic depression of the respiratory delta psi with CF3OPhzC(CN)2 and either rotenone or KCN. 3. Antimycin A, at a concentration which strongly inhibited the photosynthetic electron transport chain, only slightly lowered the light-induced delta psi in anaerobic cell suspensions. Antimycin and CF3OPhzC(CN)2 synergistically lowered delta psi generated by illumination. 4. The light-induced delta psi in anaerobic cells was only about 1.5-times larger than the respiratory-induced delta psi in darkened cells. Nevertheless it required approximately 16-times more CF3OPhzC(CN)2 to collapse the photosynthetic delta psi than the respiratory delta psi. 5. These results are discussed with reference to the ionic current/delta psi relation described in [J.B. Jackson (1982) FEBS Lett. 139, 139-143]. The unifying feature is that the intrinsic conductance of the cell membrane is strongly dependent on delta psi but the conductance due to CF3OPhzC(CN)2 is independent of delta psi.

Antimycin A↗
PubMed1983

Interaction between the respiratory and photosynthetic electron transport chains of intact cells of Rhodopseudomonas capsulata mediated by membrane potential.

1. The inhibition of respiration by light and the relief from this inhibition by uncoupling agents have been studied in intact cells of Rhodopseudomonas capsulata. 2. The same concentration range of carbonylcyanide p-trifluoromethoxyphenylhydrazone [CF3OPhzC(CN)2] prevented light-inhibition of respiration and depressed the membrane potential (delta psi) in illuminated, aerobic bacterial suspensions. 3. For a wide range of CF3OPhzC(CN)2 concentration the dependence of the respiration rate on delta psi in darkened cells coincided with that in illuminated cells. 4. When present separately, antimycin A and low concentrations of CF3OPhzC(CN)2 had little effect on light-inhibition of respiration or on delta psi in illuminated, aerobic cells, but added together they gave relief from light-inhibition and they lowered delta psi. 5. In the absence of CF3OPhzC(CN)2 even very low light intensities were sufficient to inhibit respiration and increase delta psi. In the presence of CF3OPhzC(CN)2 much higher light intensities were necessary. 6. The results are interpreted as evidence that light-inhibition of respiration is mediated by delta psi. The modification of the response by uncouplers, inhibitors and with light intensity is critically determined by the ionic conductance properties of the membrane in accordance with the findings in [Clark, A.J., Cotton, N.P.J., and Jackson, J.B. (1983) Eur. J. Biochem. 130, 575-580].

Antimycin A↗
PubMed1983

Cloning and deletion mapping of the recF dnaN region of the Escherichia coli chromosome.

By cloning a 3.6-kb EcoRI fragment of the Escherichia coli chromosome with pBR322 we located more precisely recF relative to dnaN. By deletion mapping we localized functional recF to a 1.65-kb region of the cloned fragment and allowed rough mapping of the C terminus of dnaN. Cloned recF+, separated from functional flanking genes dnaN and gyrB, complemented chromosomal recF mutations presumably by coding for a cytodiffusible product. The protein encoded by dnaN was observed as a band on a polyacrylamide gel from minicells. Identification of a recF protein was not made.

Bacterial Proteins↗
PubMed1983

The iron status of Black and white female adolescents from eight Southern states.

Hb, hematocrit, plasma iron, and transferrin saturation were measured in approximately 1000 girls aged 12, 14, or 16 yr in eight southern states. The iron status parameters did not differ significantly among the three age groupings or between menstruating and nonmenstruating girls. Blacks had significantly lower mean Hb (p less than 0.0001), hematocrit (p less than 0.0001), and transferrin saturation (p less than 0.05) levels than whites and a greater proportion of Blacks exhibited low Hb (p less than 0.05) and low hematocrit levels (p less than 0.01). Adjusting for dietary iron intakes and per capita income levels did not adequately account for significant race differences for iron status parameters. These findings support the contention that genetic as well as environmental factors are responsible for the frequently reported Black-white differences in Hb and hematocrit levels.

Adolescent↗
PubMed1983

Lack of rise in serum prolactin following yttrium-90 interstitial irradiation for acromegaly.

We have investigated the possibility that the increase in serum PRL levels observed in patients with acromegaly treated with external irradiation could be due to damage to the hypothalamus or portal vessels, by comparing the effects of yttrium-90 interstitial irradiation, which is highly localised and does not normally extend to the hypothalamus, in a similar series of patients. Sixteen acromegalic patients treated by interstitial irradiation with yttrium-90 are described; GH fell from a mean of 131 mU/l (median 113 mU/l) to 17 mU/l (median 8 mU/l) after one year (P less than 0.001). PRL fell in the five initially hyperprolactinaemic patients (mean fall +/- SD: 39 +/- 17 micrograms/l at one year), but remained unchanged in the normoprolactinaemic group; PRL responsiveness to TRH was retained. Five, out of the seven normoprolactinaemic patients examined, were shown by in vitro studies of their pituitary biopsies, to have tumours that also synthesised or secreted PRL. These results are consistent with the hypothesis that the rise in PRL following external irradiation is the result of damage to the hypothalamus or portal vessels. A less likely explanation is that an overgrowth of radio-resistant PRL-secreting tumour cells is occurring after external irradiation, but not after yttrium-90 implantation.

Acromegaly↗