A numerical strategy for efficient modeling of the equatorial wave guide

Convection in the tropics is observed to involve a wide-ranging hierarchy of scales from a few kilometers to the planetary scales and also has a profound impact on short-term climate. The mechanisms responsible for this behavior present a major unsolved problem. A promising emerging approach to address these issues is cloud-resolving modeling. Here a family of numerical models is introduced specifically to model the feedback of small-scale deep convection on tropical planetary waves and tropical circulation in a highly efficient manner compatible with the approach through cloud-resolving modeling. Such a procedure is also useful for theoretical purposes. The basic idea in the approach is to use low-order truncation in the meriodonal direction through Gauss–Hermite quadrature projected onto a simple discrete radiation condition. In this fashion, the cloud-resolving modeling of equatorially trapped planetary waves reduces to the solution of a small number of purely zonal two-dimensional wave systems along a few judiciously chosen meriodonal layers that are coupled only by some additional source terms. The approach is analyzed in detail with full mathematical rigor for linearized equatorial primitive equations with source terms.

Guanidinium-cholesterol cationic lipids: efficient vectors for the transfection of eukaryotic cells.

Two cationic lipids, bis-guanidinium-spermidine-cholesterol (BGSC) and bis-guanidinium-trencholesterol (BGTC)-cholesterol derivatives bearing two guanidinium groups-have been synthesized and tested as artificial vectors for gene transfer. They combine the membrane compatible features of the cholesterol subunit and the favorable structural and high pKa features of the guanidinium functions for binding DNA via its phosphate groups. Reagent BGTC is very efficient for transfection into a variety of mammalian cell lines when used as a micellar solution. In addition, both BGTC and BGSC present also a high transfection activity when formulated as liposomes with the neutral phospholipid dioleoylphosphatidyl ethanolamine. These results reveal the usefulness of cholesterol derivatives bearing guanidinium groups for gene transfer.

The wing of the enhancer-binding domain of Mu phage transposase is flexible and is essential for efficient transposition.

A tetramer of the Mu transposase (MuA) pairs the recombination sites, cleaves the donor DNA, and joins these ends to a target DNA by strand transfer. Juxtaposition of the recombination sites is accomplished by the assembly of a stable synaptic complex of MuA protein and Mu DNA. This initial critical step is facilitated by the transient binding of the N-terminal domain of MuA to an enhancer DNA element within the Mu genome (called the internal activation sequence, IAS). Recently we solved the three-dimensional solution structure of the enhancer-binding domain of Mu phage transposase (residues 1-76, MuA76) and proposed a model for its interaction with the IAS element. Site-directed mutagenesis coupled with an in vitro transposition assay has been used to assess the validity of the model. We have identified five residues on the surface of MuA that are crucial for stable synaptic complex formation but dispensable for subsequent events in transposition. These mutations are located in the loop (wing) structure and recognition helix of the MuA76 domain of the transposase and do not seriously perturb the structure of the domain. Furthermore, in order to understand the dynamic behavior of the MuA76 domain prior to stable synaptic complex formation, we have measured heteronuclear 15N relaxation rates for the unbound MuA76 domain. In the DNA free state the backbone atoms of the helix-turn-helix motif are generally immobilized whereas the residues in the wing are highly flexible on the pico- to nanosecond time scale. Together these studies define the surface of MuA required for enhancement of transposition in vitro and suggest that a flexible loop in the MuA protein required for DNA recognition may become structurally ordered only upon DNA binding.