Topoisomerase III can serve as the cellular decatenase in Escherichia coli

topB, encoding topoisomerase III, was identified as a high copy suppressor of the temperature-sensitive parC1215 allele, encoding one of the subunits of topoisomerase IV. Overexpression of topoisomerase III at the nonpermissive temperature was shown subsequently to restore timely chromosome decatenation and suppress lethality in strains carrying either temperature-sensitive parE or parC alleles. By developing an assay in vitro for precatenane unlinking, we demonstrated directly that both topoisomerase III and topoisomerase IV were efficient at this task, whereas DNA gyrase was very inefficient at precatenane removal. These observations suggest that precatenane unlinking is sufficient to sustain decatenation of replicating daughter chromosomes in the cell.     

Breast cancer found at the time of breast reduction.

In a recent study involving 27,500 women who had breast reduction surgery in Ontario, Canada, 17 women who were diagnosed as having breast cancer at the time of their breast reduction surgery were identified. The aims of this study were to (1) describe a population-based series of patients who had breast cancer diagnosed at the time of breast reduction, (2) describe the treatment of these cancers, and (3) compare their survival rate with survival in patients in the general population who had breast cancer. Information about these women, their treatment, and outcome was extracted from hospital records, pathology reports, and reports from regional cancer centers. The chance of finding an invasive breast cancer at the time of breast reduction was 0.06 percent, which is lower than what has been reported previously. Sixty-seven percent of these women were treated with total mastectomy. In the remaining 33 percent, who were treated with partial mastectomy, the entire tumor was removed at the time of breast reduction. Fifty percent of the women were treated with radiation, and 25 percent were treated with chemotherapy or hormonal therapy. Compared with women in the general population of Ontario who have breast cancer, women whose breast cancer is discovered during breast reduction surgery are more likely to be treated with complete mastectomy and less likely to be treated with radiotherapy or chemotherapy. Seventy-one percent of the breast reduction group were axillary node-negative at diagnosis, compared with 58 percent in the general population of women with breast cancer. Survival from breast cancer in women diagnosed at the time of breast reduction (88 percent, 5-year survival) was better than survival from breast cancer in the general population (77 percent). These findings suggest that cancers found in women at the time of breast reduction are less advanced, possibly because they are diagnosed at an earlier stage.     

Human natural killer cell adhesion molecules. Differential expression after activation and participation in cytolysis.

Cell adhesion molecules (CAM) participate in interactions between lymphocytes, accessory cells, and target cells that are critical in the generation of effective immune responses. To characterize the involvement of CAM in NK and lymphokine activated killer (LAK) activities, we examined the expression of several CAM by freshly isolated human NK cells and by NK cells activated in vitro with IL-2, and compared this to CAM expression by T lymphocytes under similar conditions. Freshly isolated human NK cells were uniformly LFA-3 (CD58)+ and expressed two to three-fold higher surface levels of LFA-1 (CD11a/CD18) than resting T lymphocytes. More NK cells than T cells also expressed phenotypically detectable levels of intercellular adhesion molecule-1 (CD54). After in vitro incubation with IL-2, human NK cells demonstrated four- to sixfold increases in surface levels of CD11a/CD18, CD2, CD54, CD58, and the NK cell-associated Ag NKH-1 (CD56). Furthermore, essentially all NK cells became CD54+ within 3 days of exposure to IL-2. T cells did not demonstrate comparable up-regulation of CAM after incubation with IL-2. Increases in NK cell CAM expression were associated with enhanced formation of E:T cell conjugates, enhanced killing of NK-sensitive targets, and the induction of cytotoxicity for previously NK-resistant targets (LAK activity). The LAK activity induced by exogenous IL-2 could be partially inhibited by anti-CD2, anti-CD11a, or anti-CD54 antibodies and almost completely abrogated by anti-CD2 and anti-CD11a in combination. These studies suggest that CAM play a central role in the regulation of NK cytolysis, and that changes in CAM expression may alter the target cell specificity of activated NK effectors.     

Repeated measures random forests (RMRF): Identifying factors associated with nocturnal hypoglycemia

Nocturnal hypoglycemia is a common phenomenon among patients with diabetes and can lead to a broad range of adverse events and complications. Identifying factors associated with hypoglycemia can improve glucose control and patient care. We propose a repeated measures random forest (RMRF) algorithm that can handle nonlinear relationships and interactions and the correlated responses from patients evaluated over several nights. Simulation results show that our proposed algorithm captures the informative variable more often than naïvely assuming independence. RMRF also outperforms standard random forest and extremely randomized trees algorithms. We demonstrate scenarios where RMRF attains greater prediction accuracy than generalized linear models. We apply the RMRF algorithm to analyze a diabetes study with 2524 nights from 127 patients with type 1 diabetes. We find that nocturnal hypoglycemia is associated with HbA1c, bedtime blood glucose (BG), insulin on board, time system activated, exercise intensity, and daytime hypoglycemia. The RMRF can accurately classify nights at high risk of nocturnal hypoglycemia.     

Chromosomal initiation in Bacillus subtilis may involve two closely linked origins

Summary When the dnaB37 initiation mutant of Bacillus subtilis is returned to a permissive temperature following a period at 45° C, a synchronous round of DNA replication immediately ensues. Using this system we have been able to analyse the first fragments to be replicated while avoiding the use of thymine starvation or inhibitors of DNA replication. Such treatments are necessary to achieve even modest synchrony in germinating spores. Our results showed that the first fragment to be replicated was a 4kb BamHI-SalI restriction fragment, BS6. In contrast, when the analysis was performed out in the presence of novobiocin, an inhibitor of DNA gyrase, replication from BS6 was inhibited and the first fragment to be replicated was BS5, a 5.6 kb fragment located 1.7 kb to the right of BS 6. Replication from both putative origins was suppressed by rifamycin and was dependent upon dnaB. The results are discussed in relation to previous attempts to identify the first replicating fragment in germinating spores. We also discuss the possibility that B. subtilis contains two origins and suggest that either can act as the primary origin under certain conditions, or alternatively that both origins may act in concert in normal bidirectional replication, each site being required for the leading strand in each direction.     

1H-NMR study of mobility and conformational constraints within the proline-rich N-terminal of the LC1 alkali light chain of skeletal myosin. Correlation with similar segments in other protein systems

Analysis by 1H-NMR spectroscopic techniques of the conformation of the N-terminal segment of the LC1 alkali light chain of rabbit skeletal muscle has shown that this portion of the molecule adopts a well-defined elongated configuration. This rod-like feature is a consequence of the Ala/Pro-rich composition and the functional aspects of such conformational preference in this and similar segments in other proteins are discussed.     

Tin compounds inhibit the plasma cell response to metallic tin

Injection of metallic tin powder causes intense proliferation of plasma cells in draining lymph nodes of Lewis rats. Pretreatment orally with soluble tin salts prevents this response to subsequently injected metallic tin. In the present work, pretreatment with tin salts by parenteral injection was just as effective as addition to the drinking water. This new approach made the following experiments possible. Poorly soluble tin compounds were found to be inhibitory when injected parenterally. Tin salts injected parenterally into one of two rats joined in parabiotic union prevented the plasma cell response to metallic tin in both parabionts. The transfer of the inhibitory effect via the cross-circulating blood represents significant progress toward understanding the mechanisms involved. The evidence suggests the possibility that tin salts elicit an intermediary substance or process that is responsible for inhibition of the plasma cell response to metallic tin.     

Ascorbic acid regulation of norepinephrine biosynthesis in isolated chromaffin granules from bovine adrenal medulla

The effect of ascorbic acid on the conversion of dopamine to norepinephrine was investigated in isolated chromaffin granules from bovine adrenal medulla. Ascorbic acid was shown to double the rate of [3H]norepinephrine formation from [3H]dopamine, despite no demonstrable accumulation of ascorbic acid into chromaffin granules. The enhancement of norepinephrine biosynthesis by ascorbic acid was dependent on the external concentrations of dopamine and ascorbate. The apparent Km of the dopamine beta-hydroxylation system for external dopamine was approximately 20 microM in the presence or absence of ascorbic acid. However, the apparent maximum velocity of norepinephrine formation was nearly doubled in the presence of ascorbic acid. By contrast, the apparent Km and Vmax of dopamine uptake into chromaffin granules were not affected by ascorbic acid. Norepinephrine formation was increased by ascorbic acid when the concentration of ascorbate was 200 microM or higher; a concentration of 2 mM appeared to induce the maximal effect under the experimental conditions used here. The effect of ascorbic acid on conversion of dopamine to norepinephrine required Mg-ATP-dependent dopamine uptake into chromaffin granules. In contrast to ascorbic acid, other reducing agents such as NADH, glutathione, and homocysteine were unable to enhance norepinephrine biosynthesis. These data suggest that ascorbic acid provides reducing equivalents for hydroxylation of dopamine despite the lack of ascorbate accumulation into chromaffin granules. These findings imply the functional existence of an electron carrier system in the chromaffin granule which transfers electrons from external ascorbic acid for subsequent intragranular norepinephrine biosynthesis.