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M McClelland

Publications and source records attributed to M McClelland.

At least 127 records · Page 7Linked to original sources
PubMed1987

Restriction endonucleases for pulsed field mapping of bacterial genomes.

Fundamental to many bacterial genome mapping strategies currently under development is the need to cleave the genome into a few large DNA fragments that can be resolved by pulsed field gel electrophoresis. Identification of endonucleases that infrequently cut a genome is of key importance in this process. We show that the tetranucleotide CTAG is extremely rare in most bacterial genomes with G+C contents above 45%. As a consequence, most of the sixteen bacterial genomes we have tested are cleaved less than once every 100,000 base pairs by one or more endonucleases that have CTAG in their recognition sequences: Xba I (TCTAGA), Spe I (ACTAGT), Avr II (CCTAGG) and Nhe I (GCTAGC). Similarly, CCG and CGG are the rarest trinucleotides in many genomes with G+C content of less than 45%. Thus, Sma I (CCCGGG), Rsr II (CGGWCCG), Nae I (GCCGGC) and Sac II (CCGCGG) are often suitable endonucleases for producing fragments that average over 100,000 base pairs from such genomes. Pulsed field gel electrophoresis of the fragments that result from cleavage with endonucleases that cleave only a few times per genome should assist in the physical mapping of many prokaryotic genomes.

Base Composition↗
PubMed1987

Sequences that adopt non-B-DNA conformation in form V DNA as probed by enzymic methylation.

pBR322 form V DNA is a highly torsionally strained molecule with a linking number of zero. We have used sequence-specific DNA methylases as probes for B-DNA in this molecule, exploiting the inability of methylases to methylate single-stranded DNA and Z-DNA, both of which are known to occur in form V DNA. Some sequences in form V DNA were shown to be totally in the B-form, others were totally in an altered, unmethylatable conformation, while still other sites appeared to exist partly in altered and partly in normal B-conformation. Some potential Z-forming sequences (alternating pyrimidine/purine) of less than seven base-pairs were not in the Z conformation in form V DNA, whereas others did adopt an altered structure, indicating a modulating influence of flanking sequences. Furthermore, regions of imperfect alternating pyrimidine/purine structure were sometimes capable of adopting an altered structure. In addition, some regions of altered structure had no apparent Z-forming sequences, nor were they in polypurine stretches, which have also been proposed to form left-handed DNA. These non-B-DNA conformations may represent novel left-handed helical structures or sequences that become single stranded under torsional strain. Long regions of either altered (unmethylatable) DNA or B-DNA were not always observed. In fact, one region showed three transitions between B-like DNA and altered structure within 26 base-pairs.

Base Sequence↗
PubMed1987

A conceptual model for educating primary care providers in the diagnosis and treatment of depression.

Primary care physicians consistently have been found to under-recognize or misdiagnose depressive disorders. However, it remains unclear whether diagnostic accuracy is related to the physician's knowledge base, interviewing skills and behavior, problem solving ability, and/or attitudes towards these disorders. As strategies are contemplated for improving physician recognition of depression, it is clear that psychiatric education must be guided by a comprehensive conceptual model. Such a model is proposed based upon the several educational domains intrinsic to the mastery of clinical diagnosis.

Attitude of Health Personnel↗
PubMed1987

Augmentation of the Oswestry Parawalker orthosis by means of surface electrical stimulation: gait analysis of three patients.

The Oswestry 'Parawalker' orthosis has been supplied to 15 adult thoracic level complete paraplegic patients enabling them to achieve a reciprocal gait with an inherent low energy demand. In order to further off-load the work demands on the upper limb girdle musculature during ambulation, three of these patients have undergone electrical stimulation of the gluteal muscles in stance phase. This was shown to increase the stability of the adduction and also provided forward propulsion by driving the stance-leg into extension. Bilateral stimulation of the quadriceps muscles has been shown to facilitate standing and sitting in the orthosis. Using a Kistler force platform, the crutch impulse can be seen to be reduced by as much as 36%. We speculate that this leads to a similar order of reduction in the work done by the upper limbs in these patients.

Adult↗
PubMed1987

Enhancement of the apparent cleavage specificities of restriction endonucleases: applications to megabase mapping of chromosomes.

We have described how DNA methylases may be used to enhance the apparent specificities of restriction endonucleases [9-11, 17, 18] to generate DNA fragments averaging 6000 to 270,000,000 base pairs on random DNA. Taking into account the non-random arrangement of natural DNA, we have predicted the rarity of certain recognition sequences in the genomes of several species.

Base Sequence↗
PubMed1987

Recognition of alcoholism and substance abuse in primary care patients.

Alcohol and other substance abuse are frequently seen in primary medical practice but are underdiagnosed. Forty-two (14%) of 294 adult primary care patients suffered from alcohol or other substance abuse, as diagnosed by a structured psychiatric interview. Primary care physicians identified 17 (40%) of these patients, as well as another patient identified during a six-month follow-up period, as having a substance abuse problem at initial clinical evaluation. Clinically identified substance abusers were older, more likely to be married, and more often used multiple drugs. They more frequently had antisocial personality disorders, while patients not clinically recognized were often depressed. Logistic regression analysis indicated that the presence of antisocial personality, the absence of a coexisting depressive disorder, and better social functioning scores were the factors most strongly associated with clinical recognition. The study suggests clinical judgment issues, which may be useful to physicians in training to improve their recognition and treatment of substance abuse disorders.

Alcoholism↗
PubMed1986

Psychiatric decision making in family practice. Future research directions.

Psychiatric illnesses in family practice are significantly underdiagnosed because of factors associated with both the physician and patient. Clinicians too often fail to utilize a biopsychosocial approach in the assessment process, tending to assess symptoms as organic regardless of their etiology. Patients similarly tend to emphasize the physical nature of their complaints when presenting in medical settings. Efforts have been made to improve the physician's diagnostic accuracy through the use of screening scores. The results, however, are inconclusive. It remains unclear whether the physician disregards this information or considers it irrelevant. We suggest that future research investigate not only the accuracy of the clinician's diagnostic formulation but also the processes whereby the family practitioner elicits, analyzes, and synthesizes or discards cues pertinent to mental illness. By combining statistical analyses with the analytic techniques developed in studies of medical decision making and general problem solving, detailed leads should emerge for the design of improved didactic and experiential training programs.

Attitude of Health Personnel↗
PubMed1985

Purification of Mbo II methylase (GAAGmA) from Moraxella bovis: site specific cleavage of DNA at nine and ten base pair sequences.

The restriction modification methylase M. Mbo II has been purified using a sensitive oligonucleotide linker assay. The enzyme methylates the Mbo II recognition sequence* GAAGA at adenine to produce GAAGmA. M. Mbo II can be used in conjunction with the methylation dependent restriction endonuclease Dpn I (GmATC) to produce cleavage at the 10 base sequence GAAGATCTTC. When M. Mbo II is used in combination with M. Cla I (ATCGATCGAT), cleavage by Dpn I occurs at the four ten base sequences GAAGATCTTC, GAAGATCGAT, ATCGATCTTC and ATCGATCGAT, which is equivalent to a nine base recognition site. The use of combinations of adenine methylases and Dpn I to generate highly selective DNA cleavages at a variety of sequences up to fourteen base pairs is discussed.

Base Sequence↗
PubMed1985

Assessing depression in primary medical and psychiatric practices.

A two-stage assessment of newly admitted outpatients at community mental health centers and primary medical care centers found the Center for Epidemiological Studies Depression Scale to be highly sensitive but relatively nonspecific when compared with assessments of depression by the Diagnostic Interview Schedule. Considerably higher than usual screening scores are recommended with both patient populations to improve the efficiency of the Center for Epidemiological Studies Depression Scale. The reasons for our finding that primary care clinicians underdiagnose depressive disorder while psychiatric clinicians overdiagnose it relative to the Diagnostic Interview Schedule include varied presentations by each sector's patients, differing clinical acumen, and factors affecting third-party reimbursement.

Adult↗
PubMed1984

Site-specific cleavage of DNA at 8- and 10-base-pair sequences.

A method is described for cutting DNA at specific sites that are 8 and 10 base pairs long. The DNA is first treated with a specific methylase, either the restriction-modification enzyme M. Taq I, which converts the 4-base sequence T-C-G-A to T-C-G-mA, or the similar enzyme M. Cla I, which converts the 6-base sequence A-T-C-G-A-T to A-T-C-G-mA-T. The DNA is then cleaved with Dpn I, a restriction endonuclease that recognizes the sequence G-mA-T-C. Dpn I is unique in that it cuts only DNA that is methylated at adenine in both strands of its recognition sequence. In DNAs that are not otherwise methylated at adenine in both strands of the sequence G-A-T-C, cleavage by Dpn I occurs only at the following sequences: in the case of M. Taq I methylation, 5' T-C-G-mA - T-C-G-mA 3' 3' mA-G-C - T-mA-G-C - T 5'; in the case of M. Cla I methylation, 5' A - T-C-G-mA - T-C-G-mA-T 3' 3' T-mA-G-C - T-mA-G-C - T-A 5'. Specific cutting and cloning at these methylase/Dpn I-generated sites is shown experimentally. Further, we describe how the above technique can be extended to generate Dpn I cleavage sites of up to 12 base pairs. In DNA that contains equal amounts of each base distributed at random, 8- and 10-base-pair recognition sequences occur, on the average, approximately once every 65,000 and 1,000,000 base pairs, respectively. Potential applications, including the development of cloning vectors and a rapid method for chromosome walking, are discussed.

Base Composition↗
PubMed1983

The frequency and distribution of methylatable DNA sequences in leguminous plant protein coding genes.

Methylation of higher plant DNA occurs at up to 25% of all cytosines, primarily in the sequences CpG2 and CpNpG, both of which are over 80% methylated in wheat and tobacco (Gruenbaum et al 1981). CpG and CpNpG frequencies and distributions in the known sequences of cloned genes of leguminous plants were analyzed. In this sample CpG occurred at only 49% of the frequency expected if the bases were distributed at random. This lower frequency may be attributed to the fixation of mutations generated by a high rate of deamination of 5methylcytosine to thymine (Salser 1977). Consistent with this hypothesis, the product of CpG transitions, TpG and CpA, were significantly above their expected frequency. However CpNpG occurred at approximately expected levels and there was no significant increase in its transition products CpNpA and TpNpG. Possible explanations for this phenomenon are discussed. An analysis of the distribution of di- and trinucleotides across functionally classified regions of genes showed CpG to be asymmetrically distributed. CpG was on average significantly enriched in the 3' flanking regions compared to other regions. This may reflect a methylation-mediated regulatory role for this region in some legume genes.

Base Sequence↗