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Biomedical subjects

C M Thomas

Publications and source records attributed to C M Thomas.

At least 127 records · Page 7Linked to original sources
PubMed1994

Complete nucleotide sequence of Birmingham IncP alpha plasmids. Compilation and comparative analysis.

The IncP alpha promiscuous plasmid (R18, R68, RK2, RP1 and RP4) comprises 60,099 bp of nucleotide sequence, encoding at least 74 genes. About 40 kb of the genome, designated the IncP core and including all essential replication and transfer functions, can be aligned with equivalent sequences in the IncP beta plasmid R751. The compiled IncP alpha sequence revealed several previously unidentified reading frames that are potential genes. IncP alpha plasmids carry genetic information very efficiently: the coding sequences of the genes are closely packed but rarely overlap, and occupy almost 86% of the genome's nucleotide sequence. All of the 74 genes should be expressed, although there is as yet experimental evidence for expression of only 60 of them. Six examples of tandem-in-frame initiation sites specifying two gene products each are known. Two overlapping gene arrangements occupy different reading frames of the same region. Intergenic regions include most of the 25 promoters; transcripts are usually polycistronic. Translation of most of the open reading frames seems to be initiated independently, each from its own ribosomal binding and initiation site, although, a few cases of coupled translation have been reported. The most frequently used initiation codon is AUG but translation for a few open reading frames begins at GUG or UUG. The most common stop-codon is UGA followed by UAA and then UAG. Regulatory circuits are complex and largely dependent on two components of the central control operon. KorA and KorB are transcriptional repressors controlling at least seven operons. KorA and KorB act synergistically in several cases by recognizing and binding to conserved nucleotide sequences. Twelve KorB binding sites were found around the IncP alpha sequence and these are conserved in R751 (IncP beta) with respect to both sequence and location. Replication of IncP alpha plasmids requires oriV and the plasmid-encoded initiator protein TrfA in combination with the host-encoded replication machinery. Conjugative plasmid transfer depends on two separate regions occupying about half of the genome. The primary segregational stability system designated Par/Mrs consists of a putative site-specific recombinase, a possible partitioning apparatus and a post-segregational lethality mechanism, all encoded in two divergent operons. Proteins related to the products of F sop and P1 par partitioning genes are separately encoded in the central control operon.

Amino Acid Sequence↗
PubMed1994

Differential screening of mitochondrial cDNA libraries from male-fertile and cytoplasmic male-sterile sugar-beet reveals genome rearrangements at atp6 and atpA loci.

As part of a strategy to define differences in genome organization and expression between cytoplasmic male-sterile (CMS) and male-fertile (MF) sugar-beet mitochondria, cDNA libraries from both mitochondrial genotypes were constructed. Preliminary screening with ribosomal RNA gene probes identified candidate cDNA clones corresponding to structural genes. In addition, reciprocal hybridization experiments were performed using labelled first-strand cDNA to identify uniquely transcribed sequences. One cDNA clone (pYC700) is unique to CMS mitochondria and is located upstream of the F0F1-ATPase subunit 6 gene (atp6). Another cDNA clone (pYC130), when used as a probe in northern hybridization analysis, revealed novel transcript profiles in CMS sugar-beet mitochondria. Sequence analysis of this cDNA showed strong homology with the F0F1-ATPase subunit alpha (atpA) coding sequences from several higher plants. The atp6 and atpA loci from each genotype were cloned and the genomic organization, DNA sequence and transcription of each locus was studied. Differences in the transcript profiles of each gene are a consequence of genomic rearrangements 5' to the coding sequence.

Amino Acid Sequence↗
PubMed1994

The effects of single oral doses of 17 beta-oestradiol and progesterone on finger skin circulation in healthy women and in women with primary Raynaud's phenomenon.

The effects of sex, the menstrual cycle, oral contraceptives, pregnancy, and the menopause on skin perfusion in healthy women and in patients with Raynaud's phenomenon suggest a role of female sex hormones. However, no clear relation between skin blood flow and circulating concentrations of oestrogens or progestogens has yet been found. The aim of this study was to investigate the effect of orally administered 17 beta-oestradiol and progesterone on finger skin blood flow before and during heat and cold challenge in 17 healthy normotensive women and in 12 women with Raynaud's phenomenon. In each subject standardized finger heating (45 degrees C water bath, 10 min) and cooling tests (15 degrees C water bath, 5 min and 20 min recovery) were performed twice on the second (or third) day of two consecutive menstrual cycles. 17 beta-Oestradiol (9 mg) or progesterone (300 mg) were given before the second test, after a first test with placebo. Both hormonal doses resulted in (high) physiological concentrations. Fingertip skin temperature and laser Doppler flux were measured. There were no significant differences in the test results after placebo and after progesterone. Although values of fingertip skin temperature and laser Doppler flux after 17 beta-oestradiol tended to be higher only the precooling values in the healthy subjects reached significance: fingertip skin temperature respectively with placebo and with oestradiol (mean (SD)): 32.7 (1.0) and 33.1 (0.8) degrees C; laser Doppler flux with placebo and with oestradiol: 33.6 (11.7) and 42.2 (9.5) perfusion units; both P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1994

Analysis of the chromosomal distribution of transposon-carrying T-DNAs in tomato using the inverse polymerase chain reaction.

We are developing a system for isolating tomato genes by transposon mutagenesis. In maize and tobacco, the transposon Activator (Ac) transposes preferentially to genetically linked sites. To identify transposons linked to various target genes, we have determined the RFLP map locations of Ac- and Dissociation (Ds)-carrying T-DNAs in a number of transformants. T-DNA flanking sequences were isolated using the inverse polymerase chain reaction (IPCR) and located on the RFLP map of tomato. The authenticity of IPCR reaction products was tested by several criteria including nested primer amplification, DNA sequence analysis and PCR amplification of the corresponding insertion target sequences. We report the RFLP map locations of 37 transposon-carrying T-DNAs. We also report the map locations of nine transposed Ds elements. T-DNAs were identified on all chromosomes except chromosome 6. Our data revealed no apparent chromosomal preference for T-DNA integration events. Lines carrying transposons at known map locations have been established which should prove a useful resource for isolating tomato genes by transposon mutagenesis.

Base Sequence↗
PubMed1994

Maternal hyperhomocysteinemia: a risk factor for neural-tube defects?

The maternal vitamin status, especially of folate, is involved in the pathogenesis of neural-tube defects (NTDs). Maternal folate administration can prevent these malformations. The precise metabolic mechanism of the beneficial effect of folate is unclear. In this study we focus on homocysteine accumulation, which may derive from abnormalities of metabolism of folate, vitamin B12, and vitamin B6. We studied nonpregnant women, 41 of whom had given birth to infants with NTDs and 50 control women who previously had normal offspring. The determinations included the plasma total homocysteine both in the fasting state and 6 hours after the ingestion of a methionine load. In addition, we measured the fasting blood levels of folate, vitamin B12, and vitamin B6. The mean values for both basal homocysteine and homocysteine following a methionine load were significantly increased in the group of women who previously had infants with NTDs. In nine of these subjects and two controls, the values after methionine ingestion exceeded the mean control by more than 2 standard deviations. Cystathionine synthase levels in skin fibroblasts derived from these methionine-intolerant women were within the normal range. Our findings suggest a disorder in the remethylation of homocysteine to methionine due to an acquired (ie, nutritional) or inherited derangement of folate or vitamin B12 metabolism. Increased homocysteine levels can be normalized by administration of vitamin B6 or folate. Therefore, we suggest that the prevention of NTDs by periconceptional folate administration may effectively correct a mild to moderate hyperhomocysteinemia.

Adult↗
PubMed1994

Factors influencing the risk of abnormal pregnancy outcome in epileptic women: a multi-centre prospective study.

We studied pregnancy outcome in preconceptionally recruited epileptic and control women in a multi-centre prospective non-intervention study at two university hospitals and three general hospitals. We evaluated 225 singleton pregnancies: 119 pregnancies of epileptic women who received either antiepileptic drugs (AEDs) (n = 99) or not (n = 20), and 106 pregnancies of controls. The main outcome measures were abnormal pregnancy outcome: major and minor congenital malformations, ectopic pregnancies, abortions; neonatal headcircumference; birth weight and birth length. Epileptic women had a two-fold risk of having an abnormal pregnancy outcome or an infant with minor malformations compared to healthy controls (odds ratio, with 95% confidence interval, respectively 2.1 (1.1, 4.0) and 2.0 (1.0, 4.0)). A significant correlation between the prevalence of abnormal pregnancy outcome and duration of epilepsy and AED treatment was found (risk increased by 9% (6%, 16%) per annum). No significant effect in terms of the type, the number or the serum level of the AEDs could be established. The head circumference of infants of epileptic mothers was significantly smaller (0.7 (1.2, 0.28 cm) compared to controls. An effect on the outcome of pregnancy of maternal folate supplementation or of folate blood concentrations during the periconceptional period and first trimester of pregnancy could not be determined. The severity of maternal epilepsy and/or AED treatment influences pregnancy outcome.

Abnormalities, Drug-Induced↗
PubMed1994

CA-125 levels in cervical mucus during the menstrual cycle.

OBJECTIVE: To determine CA-125 levels in cervical mucus (CM) during the menstrual cycle and their relationship to gonadal steroids and ovulation. DESIGN: Prospective study. SETTING: Two academic tertiary referral centers. PARTICIPANTS: Thirteen women with a normal fertility work-up. INTERVENTIONS: CA-125 and protein concentrations were measured in CM aspirated from the endocervical canal on alternate days in the early follicular and luteal phases and on a daily basis during the periovulatory period. Results were correlated with hormonal determinations, serum CA-125 levels, and ultrasound examination. RESULTS: Twenty ovulatory nonconceptional cycles were analyzed. Although the mean (+/- SD) concentration of CA-125 in CM (173,900 +/- 128,900 arbitrary U/mL) appeared relatively constant along the cycle, a large variation among the different samples was observed, ranging from 9,000 to 830,000 arbitrary U/mL. No clear trend could be detected as related to hormonal changes and ovulation. However, when the mucus CA-125 concentration was multiplied by the total volume of the correspondent sample, a clear periovulatory increase of total CA-125 levels was found. This was further supported by a similar trend showed by the calculated CA-125:protein concentration ratio. CONCLUSIONS: CA-125 is present in CM in high concentrations that vary widely along the cycle. Although no cyclical variation in CA-125 concentration could be determined, there was an apparent increase of total CA-125 levels parallel to the augmented mucus production during the periovulatory period. This further suggests a possible involvement of this glycoprotein in the secretory process of endocervical glands.

Adult↗
PubMed1994

Circulating inhibin levels in lactating and nonlactating women.

OBJECTIVE: To investigate the role of inhibin in the human puerperium, by measuring serum levels of immunoreactive inhibin in both lactating and nonlactating women. DESIGN: Prospective, comparative, open study. SETTING: Department of obstetrics and gynecology of a university hospital. PATIENTS: Fourteen healthy women who delivered at term: seven lactating women and seven nonlactating women treated with the dopamine-agonist CV 205-502. MAIN OUTCOME MEASURES: Serum immunoreactive inhibin, PRL, FSH, LH, E2, and P. RESULTS: All women showed a rapid decline of immunoreactive inhibin levels during the first postpartum days. Thereafter the pattern depended on the way of feeding. Nonlactating women, with their rapid return of pituitary and ovarian function, showed increasing immunoreactive inhibin levels to a maximum on day 24 (950 +/- 180 U/L). Lactating women did not show ovarian activity despite high FSH levels, and immunoreactive inhibin stayed on a low level (230 +/- 40 U/L on day 24). There was a significant correlation between immunoreactive inhibin and E2. CONCLUSIONS: The rapid decline of immunoreactive inhibin (elimination of placental hormone) is followed by an increase in nonlactating women (production by the maturing follicle) and by persistently low levels in lactating women. The lack of adequate levels of immunoreactive inhibin in lactating women may be an explanation of the relatively high FSH levels during lactation.

Aminoquinolines↗
PubMed1994

The phase of the menstrual cycle has no influence on the disease-free survival of patients with mammary carcinoma.

We evaluated the outcome of treatment for mammary carcinoma in 89 premenopausal women in relation to the phase of the menstrual cycle. The phase of the cycle was determined on the basis of serum concentrations of 17 beta-oestradiol and progesterone. The serum samples were collected 1 day prior to or on the day of operation. After a median follow-up of 4.1 years no significant differences in disease-free survival were found between the preovulatory (proliferative), periovulatory and post-ovulatory (luteal) groups. No differences in survival were found in these subgroups between the N0 and N1 subgroup. On the basis of this study we cannot confirm that the phase of the menstrual cycle during surgery has any effect on the eventual outcome in mammary carcinoma patients. However larger studies of this type are required before definitive conclusions can be reached.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1994

Regulation of transfer genes of promiscuous IncP alpha plasmid RK2: repression of Tra1 region transcription both by relaxosome proteins and by the Tra2 regulator TrbA.

The Tra1 region of broad host range IncP alpha plasmid RK2 encodes proteins essential for its promiscuous conjugative transfer and includes oriT, the site at which nicking occurs to initiate transfer replication. Unregulated expression of the Tra1 region genes would be likely to place a major burden on the host. To investigate the control of these genes the three transcriptional promoters from this region were cloned by PCR and inserted into xylE promoter probe vectors. The strength of traJp and traKp was estimated to be six to eightfold less than the strong trfA promoter which is required for expression of genes for vegetative replication of RK2. The traG promoter was about one-tenth the strength of the other two. These promoters are not repressed by products of the central control operon of RK2. However, traJp and traKp, which are arranged as back to back divergent promoters in the oriT region, are repressed by TraK which constitutes part of the relaxosome necessary for nicking at oriT. A second relaxosome protein, TraJ, represses traJp. traGp is not repressed by any relaxosome proteins. All three promoters are repressed by TrbA, which is encoded at the start of the trb operon containing the rest of the transfer genes (the Tra2 region). These circuits provide: (i) an autoregulatory way of ensuring production of enough relaxosome proteins without overburdening the host; and (ii) a means of coordinating expression of both blocks of transfer genes.

Bacterial Outer Membrane Proteins↗
PubMed1994

Molecular analysis of the operon which encodes the RNA polymerase sigma factor sigma 54 of Escherichia coli.

The rpoN gene (encoding the sigma factor sigma 54) of Escherichia coli was cloned and its nucleotide sequence determined. Promoter probe analysis confirmed the presence of a promoter in a 350 bp fragment covering the start of rpoN. The likely promoter was identified. The nucleotide sequence of the region extending 2.1 kb downstream of rpoN was also determined. This region contained four open reading frames encoding potential polypeptides of 10750, 17959, 32492 and 9810 Da; maxicell and T7 promoter studies showed that four polypeptides of similar molecular masses were expressed from this region. The amino acid sequence of the 17959 Da polypeptide showed homology to the enzyme IIA domains of several proteins of the bacterial sugar phosphotransferase system (PTS), and the 9810 Da polypeptide showed homology to the HPr proteins of the bacterial PTS. The proteins encoded downstream of rpoN are known to negatively regulate sigma 54 activity. The homologies therefore suggest that this effect on sigma 54 may be mediated by sequential protein phosphorylation and suggest that there is a link between signal transduction and transcription of sigma 54-dependent genes.

Amino Acid Sequence↗
PubMed1994

Cloning and sequencing of the genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum and the implications for the domain structure of the enzyme.

The genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum have been cloned using a probe constructed with the polymerase chain reaction, genomic DNA as target and oligonucleotide primers corresponding to amino acid sequence obtained from the purified soluble subunit. There is a cluster of three genes, designated pntAA, pntAB and pntB, whose translation products indicate polypeptides of 384, 139 and 464 amino acids, respectively. This contrasts with the situation in the enzymes from Escherichia coli (two polypeptides) and bovine mitochondria (one polypeptide) but there is close similarity between the sequences. PntAA is the soluble subunit of the enzyme from R. rubrum, equivalent to the relatively hydrophilic domain I that forms the N-terminal part of the alpha polypeptide of E. coli transhydrogenase and which probably contains the NAD(H)-binding site. PntAB corresponds to the strongly hydrophobic domain IIa at the C-terminus of the alpha polypeptide of the E. coli transhydrogenase. PntB corresponds to the E. coli beta polypeptide, which comprises the strongly hydrophobic domain IIb and the relatively hydrophilic domain III, thought to contain the NADP(H)-binding site. The peptide bond between PntAA-Lys237 and -Glu238 of both the denatured and the native soluble subunit is very sensitive to proteolysis by trypsin and the neighbouring peptide bond Lys227-Thr228 to cleavage by the endoproteinase Lys-C. Related sites have been reported to be sensitive to trypsin in the E. coli and bovine mitochondrial enzymes. The two tryptic fragments from the native R. rubrum soluble subunit are unable to reconstitute transhydrogenase activity to membranes depleted of the soluble subunit but they can block reconstitution by intact soluble subunit. It is suggested that this protease-sensitive region separates two subdomains and that, after trypsinolysis, at least one retains structural integrity and can dock with domains II and/or III.

Amino Acid Sequence↗
PubMed1993

A 2-year study on the beneficial effects of 17 beta-oestradiol-dydrogesterone therapy on serum lipoproteins and Lp(a) in postmenopausal women: no additional unfavourable effects of dydrogesterone.

INTRODUCTION: Postmenopausal hormone replacement therapy (HRT) has been described to reduce the risk of developing cardiovascular disease (CVD), which can be attributed at least in part to beneficial effects of oestrogens on serum lipoproteins. Little is known about a possible counteracting effect by the progestogen integrated in modern HRT regimens. OBJECTIVE: To study the possible changes in serum lipids, lipoproteins and apolipoproteins during HRT with special emphasis on the possible progestational effect. STUDY DESIGN: In an open-label longitudinal non-comparative study 23 healthy non-hysterectomized postmenopausal women were treated with continuous micronized 17 beta-oestradiol, 2 mg daily, in combination with cyclic dydrogesterone, 10 mg daily, the first 14 days of each 28-day treatment cycle. The women were followed for up to 2 years. RESULTS: After 2 years serum total cholesterol and low-density lipoprotein cholesterol had decreased by 9.0% and 18%, respectively (P < 0.01), while high-density lipoprotein cholesterol had increased by 13% (P < 0.01). The latter change was accompanied with similar increases in apolipoprotein A-I (+16%; P < 0.01) and A-II (+13%; P < 0.01), while apolipoprotein B remained unchanged. Serum very low-density lipoprotein (VLDL) cholesterol and VLDL-triglycerides increased by 28% and 21%, respectively, the latter reflecting the slight increase in serum triglycerides by 21%. These values, however, remained within the normal range. Serum lipoprotein(a) decreased by 16% (P < 0.01). All calculated atherogenic indices decreased (P < 0.01) during the study period. Serum lipids and (apo)lipoproteins did not change after withdrawal of dydrogesterone for 14 days during the combination therapy in the last cycle studied. Serum fibrinogen decreased by 8.4% (P < 0.01) in the first 12 cycles, after which it increased to 13% above baseline value (P < 0.01 vs. baseline). Antithrombin III did not change and serum glucose decreased by 5.7%. CONCLUSIONS: This HRT regimen induces (and also when given for a longer period) beneficial changes in the lipid profile, without affecting important indicators of thrombosis. Also, the glucose metabolism does not seem to be interfered with. Cyclic administration of dydrogesterone does not unfavourably affect serum lipids and (apo)lipoproteins when combined with 17 beta-oestradiol supplementation. Therefore, this combination hormone regimen can be recommended for use in HRT.

Blood Coagulation Factors↗
PubMed1993

Synthesis and evaluation of 2-pyridinone derivatives as HIV-1-specific reverse transcriptase inhibitors. 4. 3-[2-(Benzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyridin-2(1H)-one and analogues.

A new series of potent specific 2-pyridinone reverse transcriptase (RT) inhibitors was developed based on the preliminary development lead 3-[(phthalmido)ethyl]-5-ethyl-6-methylpyridin-2(1H)-one (3), a non-nucleoside derivative which exhibited weak antiviral activity in cell culture against HIV-1 strain IIIB. One compound, 3-[(benzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyridin-2(1H)-one (9,L-696,229), which was a highly selective antagonist of the RT enzyme (IC50 = 23 nM) and which inhibited the spread of HIV-1 IIIB infection by > 95% in MT4 human T-lymphoid cell culture (CIC95 = 50-100 nM), was selected for clinical evaluation as an antiviral agent.

Antiviral Agents↗