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M McClelland

Publications and source records attributed to M McClelland.

143 records · Page 8Linked to original sources
PubMed1982

Asymmetrical distribution of CpG in an 'average' mammalian gene.

The frequency and distribution of the rare dinucleotide CpG was examined in 15 mammalian genes. CpG is highly methylated at cytosine in mammalian DNA (1,2) and 5-methylcytosine (5mC) is thought to undergo a transition mutation via deamination to produce thymine (3). This would result in the accumulation of TpG and CpA and depletion of CpG during evolution (4). Consistent with this hypothesis, the gene sample of 26,541 dinucleotides contained CpG at 40% the frequency expected by base composition and the CpG transition products, TpG+CpA, were significantly elevated at 124% of expected random frequency. However, because CpG occurs at only 25% of expected random frequency in the genome, the sampled genes were considerably enriched in this dinucleotide. CpGs were asymmetrically distributed in sequences flanking the genes. 5'-flanking sequences were enriched in CpG at 135% of the frequency expected assuming a symmetrical distribution of all the CpGs in the sampled genes (p less than 0.01), while 3'-flanking regions were depleted in CpG at 40% of expected values (p less than 0.0001). This asymmetry may reflect the role of 5-methylcytosine in gene expression. In contrast the frequencies of GpC and GpT+ ApC did not differ significantly from that predicted by base composition and these dinucleotides were not asymmetrically distributed.

Animals↗
PubMed1981

Purification and characterization of two new modification methylases: MClaI from Caryophanon latum L and MTaqI from Thermus aquaticus YTI.

A method for detecting Type II modification methylases and determining their methylation site by assaying the ability of methylated DNA to be cleaved by heterologous restriction enzymes is described and applied to the isolation of the restriction modification methylases from Thermus thermophilus HB8, Thermus aquaticus YTI and Caryophanon latum L. M.TaqI is shown to have a methylation specificity identical to M.ThI (TCGmeA). M.ClaI methylates at adenine and protects a subset of TthI sites indicating that it methylates the sequence ATCGmeAT. Methylation by M.ThI also protects against cleavage by SalI, XhoI and at some HindII, AccI and MboI sites.

Adenine↗
PubMed1981

The effect of sequence specific DNA methylation on restriction endonuclease cleavage.

Sequence specific DNA methylation sometimes results in the protection of some or all of a restriction endonucleases' cleavage sites. This is usually, but not always, the result of methylation of one or both strands of DNA at the site characteristic of the corresponding "cognate" modification methylase. The known effects of sequence specific methylation on restriction endonucleases are compiled.

Base Sequence↗
PubMed1980

HgiAI: a restriction endonuclease from Herpetosiphon giganteus HP1023.

A new class II restriction endonuclease, HgiAI has been partially purified from Herpetosiphon giganteus HP1023. The enzyme activity has been characterized and shown to recognize the family of related hexanucleotide sequences (Formula: see text) where the second and fifth nucleotide pairs are A:T pairs in either orientation. Cleavage occurs as shown, to give DNA fragments with 3'-terminal tetranucleotide extensions. The recognition sites of the enzymes SacI and SstI (Formula: see text) form a subset of the recognition site of HgiAI. One of the four possible tetranucleotide 3'-extensions (cohesive ends), generated by HgiAI is identical with those generated by SacI and SstI, another is identical with that of PstI. HgiAI should be useful for molecular cloning.

Base Sequence↗
PubMed1978

Co-existence of pemphigus, anti-skeletal muscle antibody and a retroperitoneal paraganglioma.

Occasional reports have appeared in the literature describing a relationship between pemphigus vulgaris and malignancy (Krain & Bierman, 1974; Tagami et al., 1976). Carcinoma of the ovary, stomach, breast, endometrium and bronchus have all been associated with pemphigus (Krain, 1974). The association between pemphigus and thymoma is well known (Stillmand & Baer, 1972). Pemphigus has also been described in connection with various lymphoproliferative malignancies (Naysmith & Hancock, 1976). The purpose of this paper is to describe a patient who suffered from a rare retroperitoneal tumour in association with pemphigus vulgaris. His serum contained a high titre of anti-skeletal muscle antibody, although he showed no clinical manifestations of myasthenia gravis. He also had immunological manifestations suggestive of lupus erythematosus.

Antibodies↗
PubMed1978

Sensitivity of the carotid body to within-breath changes in arterial PCO2.

Respiration, sinus nerve chemoreceptor discharge, and carotid arterial pH were monitored in cats. Chemoreceptor discharge frequency showed oscillations that had a respiratory period when averaged over many respiratory cycles. These oscillations disappeared when pH oscillations of respiratory period were eliminated from the carotid arterial blood. The maximum sinus nerve discharge was associated with the most acid point of the recorded pH oscillation. Briefly increasing PCO2 by giving CO2-rich saline into the aortic root resulted in brief reduction in carotid arterial pH, and when this reduction occurred during inspiration tidal volume increased, even with a pH change no larger than the pH oscillations. However, increased chemoreceptor discharge could only be demonstrated when each pH change had twice the amplitude of the pH oscillations. Injections of fixed acid mixed with free carbonic anhydrase transiently increased chemoreceptor frequency, whereas injections of fixed acid alone had no effect. The carotid body is therefore sensitive to small rapid changes in arterial PCO2, and the pH electrode record indicates the size of the stimulus except when fixed acid changes are produced too closely upstream.

Animals↗
PubMed1977

Army nurse in Japan.

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History, 20th Century↗
PubMedDate not supplied

Selection against dam methylation sites in the genomes of DNA of enterobacteriophages.

Postreplicative methylation of adenine in Escherichia coli DNA to produce G6m ATC (where 6mA is 6-methyladenine) has been associated with preferential daughter-strand repair and possibly regulation of replication. An analysis was undertaken to determine if these, or other, as yet unknown roles of GATC, have had an effect on the frequency of GATC in E. coli or bacteriophage DNA. It was first ascertained that the most accurate predictions of GATC frequency were based on the observed frequencies of GAT and ATC, which would be expected since these predictors take into account preferences in codon usage. The predicted frequencies were compared with observed GATC frequencies in all available bacterial and phage nucleotide sequences. The frequency of GATC was close to the predicted frequency in most genes of E. coli and its RNA bacteriophages and in the genes of nonenteric bacteria and their bacteriophages. However, for DNA enterobacteriophages the observed frequency of GATC was generally significantly lower than predicted when assessed by the chi square test. No elevation in the rate of mutation of 6mA in GATC relative to other bases was found when pairs of DNA sequences from closely related phages or pairs of homologous genes from enterobacteria were compared, nor was any preferred pathway for mutation of 6mA evident in the E. coli DNA bacteriophages. This situation contrasts with that of 5-methylcytosine, which is hypermutable, with a preferred pathway to thymine. Thus, the low level of GATC in enterobacteriophages is probably due not to 6mA hypermutability, but no selection against GATC in order to bypass a GATC-mediated host function.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriophages↗
PubMedDate not supplied

Six-month outcomes for medical patients with major depressive disorders.

The courses of depressive disorders and factors affecting recovery rates among patients treated in primary medical care facilities have rarely been studied. The authors investigated the clinical status of 274 patients initially and six months after they sought care at one of three primary care sites. Through use of the highly structured Diagnostic Interview Schedule, they found that physicians assigned a depressive diagnosis to only a fourth of the patients so assessed by the structured interview. Nevertheless, the rates of persisting major depressive disorders at follow-up were found to be very similar for patients whom both the structured interview and the physician initially considered depressed and those so diagnosed by structured interview but not by the physician (25% and 31%, respectively). An analysis of factors associated with course of illness suggests that psychiatric status at the initial assessment and the number of assigned medical diagnoses rather than the physician's recognition and treatment of depression strongly predict continued affective disorder.

Adult↗
PubMedDate not supplied

Diagnosing depression among new patients in ambulatory training settings.

A research-validated instrument, based upon the Diagnostic and Statistical Manual of Mental Disorders-III, is used as a "gold standard" to compare physician assessments of depression. Twenty-seven of 294 patients (9.2 percent) presenting to three primary care clinics for the first time met clinical criteria for a depressive disorder. Although the 27 depressed patients differed from the nondepressed patients on sociodemographic characteristics, prior service utilization patterns, and clinical variables, only 7 of the 27 were diagnosed as depressed by their primary care physicians. Factors associated with accurate assessment include comment in the patient's chart of a prior psychiatric history. Many depressed patients reporting high levels of dysphoria on a screening instrument had no mood symptoms recorded on their charts.

Adult↗