[Contraception and obesity]. / Contraception et obésité.

The prevalence of obesity is increasing massively over several decades in industrialized countries. Obese women are sexually active but they use fewer contraceptive methods and are at high risk of unintended pregnancy. In addition, obesity is an important risk factor for venous thromboembolism events and arterial thrombosis (myocardial infarction and ischemic stroke). All of these data are to be considered in choosing a contraceptive method for obese women. Except depot medroxyprogesterone acetate injection, the progestin-only contraceptives (progestin only pills and etonogestrel subdermal implant) and the intra-uterine devices are the preferred contraceptive methods in obese women. The combined estrogen-progestin contraceptives (pill, patch and vaginal ring) may be proposed in very strict conditions (no other associated vascular risk factor). Obesity does not increase the risk of failure of most contraceptive methods. Bariatric surgery is a complex situation. It requires to program a possible pregnancy and contraception is needed for several months. Some bariatric surgical techniques such as by-pass can induce gastrointestinal malabsorption. In this situation, all oral contraceptives are not recommended because of a higher risk of failure.

The replication initiator protein pi of the plasmid R6K specifically interacts with the host-encoded helicase DnaB.

The replication initiator protein pi of plasmid R6K is known to interact with the seven iterons of the gamma origin/enhancer and activate distant replication origins alpha and beta (ori alpha and ori beta) by pi-mediated DNA looping. Here we show that pi protein specifically interacts in vitro with the host-encoded helicase DnaB. The site of interaction of pi on DnaB has been localized to a 37-aa-long region located between amino acids 151 and 189 of DnaB. The surface of pi that interacts with DnaB has been mapped to the N-terminal region of the initiator protein between residues 1 and 116. The results suggest that during initiation of replication, the replicative helicase DnaB is first recruited to the gamma enhancer by the pi protein. In a subsequent step, the helicase probably gets delivered from ori gamma to ori alpha and ori beta by pi-mediated DNA looping.

The contrahelicase activities of the replication terminator proteins of Escherichia coli and Bacillus subtilis are helicase-specific and impede both helicase translocation and authentic DNA unwinding.

Replication forks are arrested at sequence-specific replication termini primarily, perhaps exclusively, by polar arrest of helicase-catalyzed DNA unwinding by the terminator protein. The mechanism of this arrest is of considerable interest. This paper presents experimental evidence in support of four major points pertaining to termination of DNA replication. First, the replication terminator proteins of both Escherichia coli and Bacillus subtilis are helicase-specific contrahelicases, i.e. the proteins specifically impede the activities of helicases that are involved in symmetric DNA replication but not of those involved in conjugative DNA transfer and rolling circle replication. Second, the terminator protein (Ter) of E. coli blocks not only helicase translocation but also authentic DNA unwinding. Third, the replication terminator protein of Gram-positive B. subtilis is a polar contrahelicase of the primosomal helicase PriA of Gram-negative E. coli. Finally, the blockage of PriA-catalyzed DNA unwinding was abrogated by the passage of an RNA transcript through the replication terminator protein-terminus complex. These results are significant because of their relevance to the mechanistic aspects of replication termination.

Magnetic field-induced orientation of crystallites in powdered samples of layered compounds: explanation and application.

Magnetic field-induced orientation phenomena observed in many solid state NMR experiments of layered compounds have been explained in terms of the magnetic properties of these materials. Utilization of the effect to obtain "single crystal" spectra of powder samples leads to sensitive measurements of the NMR parameters which are otherwise not possible.