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M A Riley

Publications and source records attributed to M A Riley.

53 records · Page 3Linked to original sources
PubMed1993

Ubiquitins revisited: further examples of within- and between-locus concerted evolution.

Ubiquitin genes provide a model for studying the effects of concerted evolution on the evolution of a family of short repeated sequences. Previous work has demonstrated the occurrence of within-locus concerted evolution and raised the question of the effectiveness of between-locus concerted evolution for ubiquitin repeats. In this study comparative analysis of additional nucleotide sequences of ubiquitin tandem repeats provides further details of within-locus concerted evolution. Moreover, the availability of multiple polyubiquitin loci and ubiquitin fusion loci within a species makes possible the detection of between-locus concerted evolution. These data indicate that concerted evolution is an effective force for homogenizing repeats between, as well as within, loci.

Animals↗
PubMed1993

Positive selection for colicin diversity in bacteria.

To examine the hypothesis that colicin proteins are subject to diversity-enhancing selection, we studied the rates of synonymous, nonsynonymous, and intergenic nucleotide substitution in three pairs of closely related colicin clusters. The results indicate that the immunity gene and the immunity-binding domain of the colicin gene, which interact to provide specific immunity from the lethal action of the colicin toxin, accumulate substitutions at synonymous and nonsynonymous sites several times more rapidly than does the remainder of the colicin cluster. We suggest that this increased level of divergence, centered at the immunity protein, may be the result of the combined action of recombination and positive selection acting to increase colicin diversity in natural populations of Escherichia coli.

Bacteria↗
PubMed1993

Molecular mechanisms of colicin evolution.

This review explores features of the origin and evolution of colicins in Escherichia coli. First, the evolutionary relationships of 16 colicin and colicin-related proteins are inferred from amino acid and DNA sequence comparisons. These comparisons are employed to detail the evolutionary mechanisms involved in the origin and diversification of colicin clusters. Such mechanisms include movement of colicin plasmids between strains of E. coli and subsequent plasmid cointegration, transposition- and recombination-mediated transfer of colicin and related sequences, and rapid diversification of colicin and immunity proteins through the action of positive selection. The wealth of information contained in colicin sequence comparisons makes this an ideal system with which to explore molecular mechanisms of evolutionary change.

Amino Acid Sequence↗
PubMed1992

Nucleotide polymorphism at the xanthine dehydrogenase locus in Drosophila pseudoobscura.

Sequential polyacrylamide electrophoresis has revealed 20 allozymes of xanthine dehydrogenase (XDH) in Drosophila pseudoobscura. DNA sequence determination of seven isolates of the Xdh locus that represent six allozyme classes are presented here. Of the 5,456 sites examined, 180 are polymorphic, with 27 polymorphisms occurring at nonsynonymous, or replacement, sites. An average of nine amino acids differ between XDH allozyme classes, with 85% of the polymorphic amino acids singly represented. The level and pattern of variation observed at Xdh argue that the effective population size of the species is quite large--i.e., on the order of 2 x 10(6)--and that the populations sampled are quite ancient. In addition, as judged by two statistical tests, the levels of nucleotide polymorphism observed at Xdh are compatible with predictions from the neutral theory of molecular evolution.

Alleles↗
PubMed1992

A survey of Col plasmids in natural isolates of Escherichia coli and an investigation into the stability of Col-plasmid lineages.

A survey of colicins in the ECOR reference collection of Escherichia coli is presented. Twenty-five of the 72 ECOR strains exhibited a phenotype consistent with colicin production and E. coli isolated from human hosts were more likely to be colicinogenic than those from animal hosts. Multiple representatives of two Col plasmids, low-molecular-mass ColE1 plasmids and high-molecular-mass, conjugative ColIa plasmids were isolated from the ECOR collection and were examined with a combination of restriction fragment and Southern analysis. These data suggested that ColE1 plasmids comprise a stable (cohesive) plasmid lineage, while ColIa plasmids represent a family of distinct plasmid lineages united by the presence of the colicin Ia operon.

Bacteriocin Plasmids↗
PubMed1992

A theoretical and experimental analysis of bacterial growth in the bladder.

A mathematical model of human micturition dynamics and bacterial growth predicts the population growth rate required for a bladder infection to become established in the absence of adhesin-mediated surface growth. Escherichia coli strains isolated from the urinary tract have significantly higher in vitro growth rates in urine than strains isolated from the intestinal flora. The results suggest that, for E. coli isolated from the urinary tract, adhesin-mediated surface growth may not be required for infections to become established and persist. The growth-rate differences observed between urinary tract and intestinal isolates suggests that the ability to survive and efficiently utilize the resources available in urine is an important adaptation for E. coli inhabiting the urinary tract.

Analysis of Variance↗
PubMed1989

Distinguishing the forces controlling genetic variation at the Xdh locus in Drosophila pseudoobscura.

Fifty-eight isochromosomal lines sampled from two natural populations of Drosophila pseudoobscura in California and one from Bogota, Colombia, were examined using four-cutter restriction mapping. A 4.6-kb region of the xanthine dehydrogenase locus was probed and 66 of 135 restriction sites scored were polymorphic. This predicts that on average every 12th bp would be polymorphic in this region for the genes surveyed if polymorphism occurred randomly along the coding region. In addition, there were 12 insertion/deletion polymorphisms. Forty-nine distinct haplotypes were recognized in the 58 lines examined. The most common haplotype obtained a frequency of only 5%. Measures of base pair heterozygosity (0.0097) and linkage disequilibrium lead to a predicted population size in the range of 1.2-2.4 X 10(6) for the species. High levels of recombination (including gene conversion) can be inferred from the presence of all four gametic types in the data set.

Animals↗
PubMed1989

Nucleotide sequence of the Xdh region in Drosophila pseudoobscura and an analysis of the evolution of synonymous codons.

The nucleotide sequence of the Xdh region of Drosophila pseudoobscura is presented. The Xdh gene structure and organization are compared with the homologous region in D. melanogaster. This locus is shown to have similar organization in the two species, although an additional intron and three insertion/deletion events are described for the D. pseudoobscura coding region. The encoded proteins are predicted to have very similar charges and hydrophobic/hydrophilic domains even though 11% of the amino acids are different. A gene 5' to Xdh, putative l(3)s12, is suggested from sequence similarity between the species. Synonymous differences at the Xdh locus between the two species are analyzed using a new method described in the preceding paper by Lewontin. This analysis shows that synonymous positions within the Xdh locus are evolving at very different rates, being dependent on level of codon redundancy. A comparison of synonymous divergence between D. melanogaster and D. pseudoobscura in five additional genes reveals variation in the level of synonymous substitution.

Amino Acid Sequence↗
PubMed1987

Sequence of the structural gene for xanthine dehydrogenase (rosy locus) in Drosophila melanogaster.

We determined the nucleotide sequence of a 4.6-kb EcoRI fragment containing 70% of the rosy locus. In combination with information on the 5' sequence, the gene has been sequenced in entirety. rosy cDNAs have been isolated and intron/exon boundaries have been determined. We find an open reading frame which spans four exons and would encode a protein of 1335 amino acids. The molecular weight of the encoded protein (xanthine dehydrogenase), based on the amino acid translation, is 146,898 daltons which agrees well with earlier biophysical estimates. Characteristics of the protein are discussed.

Amino Acid Sequence↗
PubMed1976

Ménière disease and cerebral impairment.

A recent series of findings based on psychological test patterns suggests that the behavioral disturbance seen in Ménière disease is, in many instances, predicated on organic cerebral impairment. If this proves to be the case, an important source would have been uncovered that could account for some of the behavioral difficulties associated with Ménière disease. The present study challenges the previous reports, suggesting that these findings emerged because of imprecise methodologic procedures. The results based on our psychological test patterns reject prior conclusions that there is demonstrable evidence for organic cerebral impairment in patients with Ménière disease.

Brain Diseases↗
PubMedDate not supplied

Investigations into the failure of dental magnets.

PURPOSE: The aim of this study was to determine the mechanisms of failure of magnets used for denture retention. MATERIALS AND METHODS: Magnets were retrieved from dentures that had failed after 4 to 18 months of clinical use. The magnets were sectioned and the failure modes were evaluated using optical or scanning electron microscopy. RESULTS: The magnetic retention system investigated consists of a neodymium-iron-boron magnet sandwiched in a stainless steel keeper, capped with a titanium dome, and sealed with epoxy resin. The diffusion of moisture through the epoxy seal and the breakdown of the encapsulating material led to corrosion of the magnet. In both cases, a loss in retention occurred as the corrosion products weakened the overall magnetic attraction. CONCLUSION: The failure of magnets may occur by either breakdown of the epoxy seal or breakdown of the encapsulating material. Both problems need to be addressed to prolong the life span of these magnets.

Corrosion↗
PubMedDate not supplied

Attachment impacts a culturally diverse population in the homecare setting.

Home intravenous therapy requires knowledge and understanding for successful outcomes. This article presents the ideas of attachment, guidance, and culturally sensitive nursing practice interventions when caring for patients who require home i.v. therapy. Culturally sensitive nursing interventions can increase a patient's ability to comprehend the treatment plan if they are presented in a familiar context. As trust is built, barriers to accurate communication between the nurse and the patient and family are removed, resulting in increased patient compliance and learning. Four case studies are presented to illustrate how nursing interventions use the cultural backgrounds of patients to develop culturally sensitive nursing interventions and to show how decisions are made based on information regarding cultural norms.

Adult↗
PubMedDate not supplied

Cancer screening in the community. Taking the show on the road.

PURPOSE: The authors describe the efforts involved in improving cancer screening of an underserved population using a mobile clinic to bring these services to the community. The background, methods, results, and implications are discussed, as are the logistics of packing, scheduling, and providing follow-up. OVERVIEW: Members of the University of Pittsburgh Cancer Institute Cancer Prevention and Early Detection Program developed a cancer screening program to serve the underserved communities in the Pittsburgh area. The African American Cancer Screening Program has presented the staff with significant challenges. The most significant of those challenges has been taking the most comprehensive screening program to the areas convenient to clients. Although coordinating staff, materials, and transportation was a challenge, the logistical problems involved were resolved, allowing for the opportunity to "take the show on the road". CLINICAL IMPLICATIONS: Because the mortality rate from some cancers is higher in black Americans, early cancer screening and detection is crucial in this population. The establishment of a mobile cancer screening clinic allows underserved communities access to these services. The physical screening, educational counseling, scheduling of mammographies and flexible sigmoidoscopies, and meticulous follow-up provided through the mobile clinic may lead to a greater awareness and reduced morbidity and mortality from cancer in these communities.

Black or African American↗