Bacteriophage Mu is the largest and most efficient transposable element known. The Mu transposase (A protein) of relative molecular mass 75,000 is a central component of the transposition machinery. We report here that the N-terminal region of Mu transposase contains two distinct DNA-binding domains, one which binds the two Mu DNA ends, and another which binds an internal operator region. This internal operator is required for the transposase-mediated synapsis and nicking of Mu ends in vitro, and stimulates transposition more than 100-fold in vivo. The orientation of the operator with respect to the ends is critical to its function, whereas its distance from the ends seems to be relatively unimportant. We propose that the operator enhances transposition by transiently interacting with the transposase and Mu DNA end(s) to form a complex in which synapsis of the ends occurs.

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Laparosocpic surgery for persistent adnexal masses in the second trimester of pregnancy is safe when performed by experienced surgeons.

Experiments on both stationary and propagating double layers and a related analytical model are described. Stationary double layers with eΔφ/kTe≳1 were produced in a multiple plasma device, in which an electron drift current was present. An investigation of the plasma parameters for the stable double layer condition is described. The particle distribution in the stable double layer establishes a potential profile, which creates electron and ion beams that excite plasma instabilities. The measured characteristics of the instabilities are consistent with the existence of the double layer. Propagating double layers are formed when the initial electron drift current is large. The slopes of the transition region increase as they propagate. A physical model for the formation of a double layer in the experimental device is described. This model explains the formation of the low potential region on the basis of the space charge. This space charge is created by the electron drift current. The model also accounts for the role of ions in double layer formation and explains the formation of moving double layers.