Saint Louis University

About: Saint Louis University is a education organization based out in St Louis, Missouri, United States. It is known for research contribution in the topics: Population & Health care. The organization has 18927 authors who have published 34895 publications receiving 1267475 citations. The organization is also known as: SLU & St. Louis University.

Robustness and the cycle of phosphorylation and dephosphorylation in a two-component regulatory system

Abstract: The EnvZ/OmpR system in Escherichia coli, which regulates the expression of the porins OmpF and OmpC, is one of the simplest and best-characterized examples of two-component signaling. Like many other histidine kinases, EnvZ is bifunctional; it phosphorylates and dephosphorylates the response regulator OmpR. We have analyzed a mathematical model of the EnvZ-mediated cycle of OmpR phosphorylation and dephosphorylation. The model predicts that when EnvZ is much less abundant than OmpR, as is the case in E. coli, the steady-state level of phosphorylated OmpR (OmpR-P) is insensitive to variations in the concentration of EnvZ. The model also predicts that the level of OmpR-P is insensitive to variations in the concentration of OmpR when the OmpR concentration is sufficiently high. To test these predictions, we have perturbed the porin regulatory circuit in E. coli by varying the expression levels of EnvZ and OmpR. We have constructed two-color fluorescent reporter strains in which ompF and ompC transcription can be easily measured in the same culture. Using these strains we have shown that, consistent with the predictions of our model, the transcription of ompC and ompF is indeed robust or insensitive to a wide range of expression levels of both EnvZ and OmpR.

Infant cancer in the U.S.: histology-specific incidence and trends, 1973 to 1992

Abstract: Background Many cancers in infants demonstrate unique epidemiologic, clinical, and genetic characteristics compared with cancers in older children. Few epidemiologic reports, however, have focused on this important age group. Methods Population-based data from the Surveillance, Epidemiology, and End Results (SEER) program were used to estimate relative frequency, incidence rates, and average annual percentage change of rates among children in their first year of life (infants) who were diagnosed with a malignant neoplasm from 1973 to 1992 (N = 1461). Results The greatest proportion of cases (12%) was diagnosed during the first month of life, with extracranial neuroblastoma accounting for 35% of this total. Overall, the average annual incidence rate was 223/1,000,000 infants. Extracranial neuroblastoma was the most common infant malignancy (58/1,000,000 infants per year), followed by leukemias (37/1,000,000), brain and central nervous system (CNS) tumors (34/1,000,000), and retinoblastoma (27/1,000,000). White infants had a 32% higher incidence rate than black infants. The average annual percentage increase in rates for all cancer from 1973 to 1992 was 2.9% (95% CI: 1.9%, 3.8%). For neoplasms with at least 100 cases, increasing trends were greatest for retinoblastoma (4.6%), CNS (4.1%), and extracranial neuroblastoma (3.4%). Conclusions Incidence rates increased notably over the study period. Future studies should consider the unique presentation of infants with cancer when developing new hypotheses related to cancer etiology and gene-environment interactions.

Born-International SMEs: BI-Level Impacts of Resources and Intentions

Abstract: The Katz and Gartner (1988) model describes four central properties of emerging organizations: resources, intention, exchange, and boundary. While designed as a general model for organizations, the approach has the potential to explain the early lives of "born-international" firms. In this study, boundary is used to define the central sampling frame. Two other properties, resources and intention, are evaluated in terms of their impact on the fourth property: exchange, measured as a firm's export growth and intensity. Given the inherent presence of two levels of analysis in emerging organizations, intention and resources are evaluated at both the individual and the organizational level. A sample (N = 47) of young "born-international" firms in the Indian software industry was studied, using a questionnaire. Results of the analysis are mixed for resources at both the individual and firm level variables. Intention is significant at the individual level but not the firm level. Contrary to other studies, these findings suggest that during the early stages of firm development, owner, not firm, characteristics play a pivotal role in performance, especially exports. The speculation is that this occurs because, in early stages, firms are relatively disorganized relative to the owner.