Invariant Distribution of Promoter Activities in Escherichia coli

Cells need to allocate their limited resources to express a wide range of genes. To understand how Escherichia coli partitions its transcriptional resources between its different promoters, we employ a robotic assay using a comprehensive reporter strain library for E. coli to measure promoter activity on a genomic scale at high-temporal resolution and accuracy. This allows continuous tracking of promoter activity as cells change their growth rate from exponential to stationary phase in different media. We find a heavy-tailed distribution of promoter activities, with promoter activities spanning several orders of magnitude. While the shape of the distribution is almost completely independent of the growth conditions, the identity of the promoters expressed at different levels does depend on them. Translation machinery genes, however, keep the same relative expression levels in the distribution across conditions, and their fractional promoter activity tracks growth rate tightly. We present a simple optimization model for resource allocation which suggests that the observed invariant distributions might maximize growth rate. These invariant features of the distribution of promoter activities may suggest design constraints that shape the allocation of transcriptional resources

Cell Lineage Analysis of the Mammalian Female Germline

Fundamental aspects of embryonic and post-natal development, including maintenance of the mammalian female germline, are largely unknown. Here we employ a retrospective, phylogenetic-based method for reconstructing cell lineage trees utilizing somatic mutations accumulated in microsatellites, to study female germline dynamics in mice. Reconstructed cell lineage trees can be used to estimate lineage relationships between different cell types, as well as cell depth (number of cell divisions since the zygote). We show that, in the reconstructed mouse cell lineage trees, oocytes form clusters that are separate from hematopoietic and mesenchymal stem cells, both in young and old mice, indicating that these populations belong to distinct lineages. Furthermore, while cumulus cells sampled from different ovarian follicles are distinctly clustered on the reconstructed trees, oocytes from the left and right ovaries are not, suggesting a mixing of their progenitor pools. We also observed an increase in oocyte depth with mouse age, which can be explained either by depth-guided selection of oocytes for ovulation or by post-natal renewal. Overall, our study sheds light on substantial novel aspects of female germline preservation and development

Childhood Sexual Abuse and Health Risk Behaviors in Patients with HIV and a History of Injection Drug Use

Childhood sexual abuse (CSA) is related to poorer health outcomes, associated with increased risk for HIV acquisition, and prevalent among HIV risk groups. Links between CSA and health behavior are an important health concern. We examined the relationship between CSA and transmission risk behavior and medication adherence in 119 HIV-infected individuals with an injection drug use history. 47% reported CSA, with no gender difference. Individuals who experienced CSA were more likely to report sexual HIV transmission risk behavior in the past 6 months, more sexual partners, use of heroin in the past 30 days, and worse adherence to HIV medication than those who did not. These findings confirm that rates of CSA are high in this population, and suggest that a history of CSA may place people managing both HIV and opioid dependence at increased risk for HIV transmission, poor adherence to medication, and vulnerability to substance use relapse

First anal intercourse and condom use among men who have sex with men in Switzerland.

The aim of this study was to analyze the circumstances of first anal intercourse (FAI) among men who have sex with men (MSM) and to identify factors associated with condom use at this event. We conducted a cross-sectional survey among a convenience sample of MSM living in Switzerland (N = 2,200). Anonymous questionnaires were distributed using Swiss gay communication channels (newspapers, associations, websites) and gay bathhouses. We gathered data on age at FAI, age of the partner, degree of familiarity with him, place of first meeting, and sociodemographic indicators. We did not ask whether FAI was insertive, receptive, or both. Data were stratified by birth year classes (birth cohorts). The median age at FAI fell from 24.5 years among men born before 1965 to 20.0 years among those born between 1975 and 1984 (p < .001). In each birth cohort, between 20 and 30% reported a partner 10 years older or more. Of eight variables examined in multivariate analysis, two were positively associated with condom use: age of participants at FAI and low degree of familiarity between partners. Conversely, large age discrepancy between partners was negatively associated with condom use. In conclusion, our data showed that early initiation of anal intercourse and large age discrepancy were associated with risk taking: a pattern of initiation that may facilitate HIV transmission from older to younger cohorts of MSM. Since age at FAI is on the decrease, there is an urgent need to heighten awareness of prevention actions regarding sexual debut of MSM

The interaction between deformation, fracture initiation and fracture propagation in two phase Co-CoAl alloys

Fracture initiation and propagation in two phase alloys containing fairly large volume fractions of nonplastically deforming inclusions have been analyzed. The Argon, Im and Safoglu treatment of fracture initiation of elastic inclusions as a result of back stresses resulting from strain accommodation of the phases has been extended to relatively large volume fractions of second phase. This allows calculation of the distribution of fractured particles as a function of alloy strain provided the fracture stress of the elastically deforming phase is known. The analysis has been applied to the Co-CoAl two phase alloy for volume fractions of CoAl ranging from about two to twenty-five pct. Quantitative metallographic analysis of fractured specimens indicates very good agreement between the measured fraction of fractured particles and those predicted from the theory without recourse to any adjustable parameters. Critical crack propagation in alloys of this type can also be analyzed on the basis of a fracture mechanics approach of Rice which was modified to consider that the crack spacing decreases with increasing strain due to cumulative hard phase cracking. The tensile strengths of the alloys can then be predicted with recourse to one adjustable parameter which varies with hard phase volume fraction. The deduced variation of this parameter with hard phase volume fraction, however, is as expected. © 1980 American Society for Metals and the Metallurgical Society of AIME