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M C Butler

Publications and source records attributed to M C Butler.

At least 19 recordsLinked to original sources
PubMed2001

On the nature of conformational openings: native and unfolded-state hydrogen and thiol-disulfide exchange studies of ferric aquomyoglobin.

Native-state amide hydrogen exchange (HX) of proteins in the presence of denaturant has provided valuable details on the structures of equilibrium folding intermediates. Here, we extend HX theory to model thiol group exchange (SX) in single cysteine-containing variants of sperm whale ferric aquomyoglobin. SX is complementary to HX in that it monitors conformational opening events that expose side-chains, rather than the main chain, to solvent. A simple two-process model, consisting of EX2-limited local structural fluctuations and EX1-limited global unfolding, adequately accounts for all HX data. SX is described by the same model except at very low denaturant concentrations and when the bulky labeling reagent 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) is used. Under these conditions SX can occur by a novel denaturant-dependent process. This anomalous behavior is not observed when the smaller labeling reagent methyl methanethiosulfonate is employed, suggesting that it reflects a denaturant-induced increase in the amplitudes of local structural fluctuations. It also is not seen in heme-free apomyoglobin, which may indicate that local openings are sufficiently large in the absence of denaturant to allow DTNB unhindered access. Differences in SX kinetics obtained using the two labeling reagents provide estimates of the sizes of local opening reactions at different sites in the protein. At all sequence positions examined except for position 73, the same opening event appears to facilitate exchange of both backbone amide and side-chain thiol groups. The C73 thiol group is exposed by a low-energy fluctuation that does not expose its amide group to exchange.

Amides↗
PubMed2001

The replication timing program of the Chinese hamster beta-globin locus is established coincident with its repositioning near peripheral heterochromatin in early G1 phase.

We have examined the dynamics of nuclear repositioning and the establishment of a replication timing program for the actively transcribed dihydrofolate reductase (DHFR) locus and the silent beta-globin gene locus in Chinese hamster ovary cells. The DHFR locus was internally localized and replicated early, whereas the beta-globin locus was localized adjacent to the nuclear periphery and replicated during the middle of S phase, coincident with replication of peripheral heterochromatin. Nuclei were prepared from cells synchronized at various times during early G1 phase and stimulated to enter S phase by introduction into Xenopus egg extracts, and the timing of DHFR and beta-globin replication was evaluated in vitro. With nuclei isolated 1 h after mitosis, neither locus was preferentially replicated before the other. However, with nuclei isolated 2 or 3 h after mitosis, there was a strong preference for replication of DHFR before beta-globin. Measurements of the distance of DHFR and beta-globin to the nuclear periphery revealed that the repositioning of the beta-globin locus adjacent to peripheral heterochromatin also took place between 1 and 2 h after mitosis. These results suggest that the CHO beta-globin locus acquires the replication timing program of peripheral heterochromatin upon association with the peripheral subnuclear compartment during early G1 phase.

Animals↗
PubMed2000

Human transaldolase-associated repetitive elements are transcribed by RNA polymerase III.

Repetitive elements flanked by exons 2 and 3 of the human transaldolase gene, thus termed transaldolase-associated repetitive elements, TARE, were identified in human DNA. Nonpolyadenylated TARE transcripts were detected by Northern blot analysis and cloned by reverse transcriptase-mediated polymerase chain reaction from human T lymphocytes. A dominant 1085-nucleotide long transcript, TARE-6, contained two adjacent Alu elements, a right monomer and a complete dimer, oriented opposite to the direction of transcription of the transaldolase gene. Reverse transcriptase-polymerase chain reaction and in vitro transcription analyses showed that transcription of TARE-6 proceeded in the orientation of the RNA pol III promoter of the Alu dimer and opposite to the orientation of the TAL-H gene. TAREs lacking RNA polymerase III promoter showed no transcriptional activity. In vitro transcription of TARE-6 was resistant to 1 microg/ml alpha-amanitin but sensitive to 100 microg/ml alpha-amanitin and tagetitoxin, suggesting involvement of RNA polymerase III. TAREs in both the transaldolase and HSAG-1 genomic loci were surrounded by TA target site duplications. Homologies between transaldolase and HSAG-1 break off internally at splice donor and acceptor sites. The results suggest RNA polymerase III-mediated transcription of TARE may be a source of repetitive elements, contributing to distinct genes and thus shaping the human genome.

Base Sequence↗
PubMed1996

Sexual behavior and vaginal colonization by group B streptococcus among minority women.

OBJECTIVE: To test the hypothesis that sexual behaviors predict colonization of the vagina by group B streptococcus among minority women. METHODS: We conducted a prospective, descriptive study of 192 consecutive African-American (37%) and Hispanic women (63%). Each woman underwent a detailed interview concerning sexual behavior. Separate specimens were taken from the endocervix, upper vagina, lower vagina, and anorectum and placed in selective broth media for isolation of group B streptococcus. Significant behavioral predictors of vaginal group B streptococcus colonization and heavy (3-4+) colonization were identified using stepwise logistic regression. RESULTS: The incidence of vaginal colonization was 39% and heavy colonization was 35%. Nineteen percent reported anal intercourse, 46% reported sex at least two times per week, and 21% reported more than one partner in the previous 30 days. The significant predictors of vaginal group B streptococcal infection were: African-American ethnicity, adjusted odds ratio (OR) 6.1 (95% confidence interval [CI] 2.5-15.1); presence of rectal group B streptococcus, adjusted OR 100.6 (95% CI 26.7-379.3); nulliparous, adjusted OR 3.6 (95% CI 1.4-9.5); and nonpregnant status, adjusted OR 3.9 (95% CI 1.3-12.2). The significant predictors of heavy colonization were: more than one partner in the last 30 days, adjusted OR 2.6 (95% CI 1.2-5.6); and African-American ethnicity, adjusted OR 2.3 (95% CI 1.2-4.5). Anal intercourse was associated with a reduced likelihood of vaginal group B streptococcal infection, adjusted OR 0.34 (95% CI 0.12-0.91). CONCLUSION: Sexual behavior, especially anal intercourse, does not predict vaginal colonization by group B streptococcus. African-American women are more likely to have vaginal and heavy group B streptococcus colonization. Heavy vaginal colonization is associated with multiple partners in African-American women.

Adult↗
PubMed1994

Evaluation of the use of an artificial teat to measure the forces applied by a milking machine teatcup liner.

An artificial teat containing a force transducer was constructed to study the forces exerted by the liner on the teat during milking. The objective was to develop a method of comparing the action of different liners under a variety of different milking conditions. The rigid structure of the artificial teat did not provide an accurate representation of a real teat but deformable models used in the past have not proved practical. Initial tests of the teat showed that it gave repeatable results during calibration. When placed in a liner, however, repeatable results could not be obtained if the teat-liner interface was disturbed. The forces that were measured under simulated milking conditions varied with liner wall position and with time. There was a peak and trough prior to a stable asymptotic value being attained and a noticeable time lag behind pulsation chamber pressure. This technique can be used to compare liners when a reliable method of locating the artificial teat within the liner has been developed.

Animals↗
PubMed1992

Characterization of a stable, reactivatable complex between chaperonin 60 and mitochondrial rhodanese.

Efficient formation of the cpn60-rhodanese complex can be achieved by mixing unfolded rhodanese with excess cpn60 at low temperature. By employing these conditions, a stable and highly reactivatable complex is formed. The complex is not formed when native enzyme is used. Concentrations of NaCl, as high as 0.75 M, do not have any effect on the formation or disruption of the binary complex. cpn60-bound rhodanese contains an exposed hydrophobic surface, as detected by the binding of the fluorescent reporter, 1-anilinonaphthalene-8-sulfonic acid. The intrinsic fluorescence of cpn60-bound rhodanese reports that the average tryptophan is in an intermediate environment between that found in unfolded and native states. This form of rhodanese has an accessibility to quenching by acrylamide or iodide that is intermediate between the unfolded and native forms of the enzyme. Protease susceptibility studies show that rhodanese bound to cpn60 exhibits a trypsin digestion pattern similar to the native enzyme, although it is more rapidly proteolyzed. The results suggest that the conformation of cpn60-bound rhodanese resembles a native-like conformation, but with increased flexibility. Further, only intact rhodanese or enzyme lacking its N-terminal sequence can interact with cpn60 and form a stable binary complex. The protein fragment corresponding to the rhodanese N-terminal sequence did not form part of a stable complex with cpn60.

Acrylamide↗
PubMed1992

The control of milk flow through the teats of dairy cows.

The effects of teat smooth muscles and pulsation on the control of rate of milk flow have been investigated in two split udder experiments during machine milking of dairy cows. When two teats were milked without pulsation, the peak flow rate was reduced by .132 kg/min for these teats and by .107 kg/min for the other two teats, which received good pulsation. Both of these reductions were statistically significant. This suggests that there is systemic control of the teat sphincter muscle. When systemic muscle control was removed by treatment with clenbuterol, a beta-agonist, all flow rates increased. However, when the proportion of the pulsation cycle for which milk flow can occur was considered, the actual flow rate for teats milked without pulsation was approximately 36% lower than that for teats milked with pulsation. This was independent of clenbuterol treatment, suggesting that this local control is independent of overall muscle tone.

Animals↗
PubMed1991

Positional influences on job satisfaction and job performance: a multivariate, predictive approach.

This study examined relationships between job attitudes, work environment perceptions, and supervisors' ratings of job performance among health care employees occupying both medical care and administrative positions in ambulatory clinic settings. Between-group differences were noted on the perceived relationship with the supervisor, level of job/role conflict, and working conditions. Results are discussed in terms of functional and dysfunctional aspects of control systems and path-goal theory of leadership.

Adult↗
PubMed1985

Effects of aminoglutethimide on cervical dilatability and serum immunoreactive relaxin in pregnant rats.

Administration of aminoglutethimide (AG) at a daily sc dose of 20 mg/kg to rats from the 10th to 20th days of pregnancy resulted in fetal wastage, increased placental weights, and decreased placental alkaline phosphatase. In an effort to determine the endocrine problems relating to these abnormalities, serum relaxin (R) and progesterone (P) levels were determined by RIA and cervical distensibility was measured: All three parameters were subnormal in AG-treated rats. Therapy with estrogen (E) or (P) failed to correct any of the physiological problems associated with AG treatment, but a combination of these steroids increased fetal survival to control levels. However, cervical dilation in preparation for parturition failed to occur. Relaxin therapy alone increased cervical dilation but did not enhance fetal survival. A combination of E, P, and R maintained a normal complement of fetuses and provided normal cervical dilation. None of the treatments prevented placental enlargement but P treatment tended to maintain normal placental alkaline phosphatase.

Aminoglutethimide↗
PubMed1984

Families' responses to chemotherapy by an ambulatory infusion pump.

A home ambulatory infusion program for cancer patients receiving chemotherapy has been found to be a cost-effective means of administering certain medications in a safe manner while increasing patient control and autonomy and the quality of life for patients and families.

Adult↗
PubMed1984

Patient and provider satisfaction in Navy family practice and non-family practice clinics.

Differences between family practice and non-family practice health care service delivery have been characterized in terms of patient satisfaction. As health care providers may often behave according to their conceptions of what is satisfying for patients, a clarification of the degree of congruence between patient self-reports and provider impressions is needed. Responses to four patient satisfaction scales were obtained from 136 providers and 1,735 patients in both family practice and non-family practice Navy clinics. Results of separate multiple discriminant analyses conducted between settings for both provider and patient groups indicated that providers emphasized trust and range of services as hallmarks of family-oriented care. Patients, alternatively, emphasized accessibility of services, whereas range of services was not relevant to differentiating between treatment modalities.

Attitude of Health Personnel↗
PubMed1983

Patient satisfaction in adjacent family practice and non-family practice Navy outpatient clinics.

Patient satisfaction was assessed in adjacent family practice and non-family practice clinics at a Naval Regional Medical Center. Results indicated that patients in the family practice clinic (n = 341) were significantly more satisfied with care than those in the other primary care clinic (n = 390). Although older people and men were generally more satisfied with care, demographic factors did not differentially affect patient preferences for the family practice approach to ambulatory care.

Adolescent↗
PubMed1981

Motivational determinants of illicit drug use: an assessment of underlying dimensions and their relationship to behavior.

Principal components analysis was used to delineate motivational patterns associated with illicit drug use in a population of U.S. Navy enlisted men (n = 867) undergoing drug rehabilitation. Patients indicated which of 31 reasons for drug use were associated with various drugs. Four components emerged from this analysis, labeled Insight-Seeking, Therapeutic Needs, Sentience, and Pleasure-Seeking. Higher order factor analysis revealed the presence of a general factor, labeled General Sensation-Seeking. Multiple regression procedures were used to relate the derived dimensions to actual drug use behavior. The significant relationships observed among the factor analytic patterns in predicting overall drug involvement were shown to lead to increased explanation concerning interrelationships among personality needs and social resources. The findings suggested a number of hypotheses pertaining to increased understanding of motivational patterns underlying initiation and continuation of illicit drug use.

Adult↗