During the last 10 years, much progress has been made in understanding signal transduction. However, the function of many newly identified proteins remains unknown. The protein/protein interactions ...have emerged as a major biochemical mechanism of signal transduction. They are of major interest to elucidate the role of a protein in one or another cellular process. The two-hybrid system is especially well designed for such investigation. Here we show that the contribution of this technique already is and will be essential in dissecting the molecular mechanism of transduction pathways in many cell types.
The Escherichia coli rap mutant inhibits vegetative growth of bacteriophage lambda. Phage mutations termed bar, which overcome the rap defect, have been mapped to three genetic loci in the pL operon. ...Plasmids with a lambda wild-type bar DNA segment cloned downstream from an active promoter cannot be maintained in rap mutant bacteria. The viability of a rap mutant strain decreases rapidly after induction of transcription through bar regions present on plasmids. Under these (restrictive) conditions the expression of plasmid-encoded beta-lactamase and plasmid DNA replication are arrested, but plasmid RNA synthesis continues for several hours. Analysis of protein extracts from E. coli rap cells containing bar plasmids revealed that both plasmid and bacterial protein synthesis are inhibited under restrictive conditions. In addition, unlike other RNAs tested, the chemical half-life of bar RNA increases 3.5-fold relative to the half-life of bar RNA under permissive conditions. We propose that transcription through the bar region, or the accumulation of bar RNA, results in an irreversible defect in cellular mRNA translation. This defect eventually kills the rap cells, and thus prevents bar plasmid maintenance.
The early stages of clot formation in blood vessels involve platelets adhesion-aggregation. Although these mechanisms have been extensively studied, gaps in their understanding still persist. We have ...performed detailed in-vitro experiments and developed a numerical model to better describe and understand this phenomenon. Unlike previous studies, we took into account both activated and non-activated platelets, as well as the 3D nature of the aggregation process. Our investigation reveals that blood albumin is a major parameter limiting platelet adhesion and aggregation. Our results also show that the well accepted Zydney-Colton shear-induced diffusivity is much too low to explain the observed deposition rate. Simulations are in very good agreement with observations and provide quantitative estimates of the adhesion and aggregation rates that are hard to measure experimentally.
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