The pattern of mutagen-induced back mutations inSalmonella typhimurium

Summary The effects of UV, diethyl sulfate, and 2-aminopurine in causing back mutations were studied with spontaneous and 2-aminopurine-induced leucine auxotrophs ofSalmonella typhimurium. A correlation was noted between the effectiveness of diethyl sulfate and 2-aminopurine. All the 2-aminopurine inducible mutants fell into two categories; those whose frequency of induced reversions were independent of the number of cell divisions following treatment and those whose frequencies were strongly dependent upon division. It was suggested that the two categories represented the two purine-pyrimidine base pairs.Almost all the 2-aminopurine induced mutants belonged to the division dependent category. From this it was inferred that 2-aminopurine paired preferentially with one of the two pyrimidine bases.This work was supported by a research grant, RG 7178, from the Division of General Medical Sciences, Public Health Service.     

Bacterial sporulation: FtsZ rings do the twist

Formation of the polar Z ring is a crucial step in the establishment of cellular asymmetry during sporulation of Bacillus subtilis. New results suggest that the transition from medial to polar Z rings involves a dynamic FtsZ spiral structure that may transfer FtsZ from medial to polar sites.     

Challenges of single-cell diagnostics: analysis of gene expression

Analysis of single-cell gene expression promises a more precise understanding of human disease pathogenesis and important diagnostic applications. Here, we review the rationale for the study of gene expression at the single-cell level, practical methods to isolate homogeneous or single-cell samples, and current approaches to the analysis of single-cell gene expression. Finally, we highlight applications of laser microdissection-based gene expression analysis to the study of human disease and clinical diagnosis.     

Bacteriophage tubulins: carrying their own cytoskeleton key

Cytoskeletal elements are well known to be widespread in eukaryotes and prokaryotes, providing important, diverse functions for cells large and small. Two new studies report that some bacteriophages encode their own tubulin homologs to facilitate phage reproduction within the host cell.     

Mutual effects of MinD-membrane interaction: II. Domain structure of the membrane enhances MinD binding

MinD, a well-conserved bacterial amphitropic protein involved in spatial regulation of cell division, has a typical feature of reversible binding to the membrane. MinD shows a clear preference for acidic phospholipids organized into lipid domains in bacterial membrane. We have shown that binding of MinD may change the dynamics of model and native membranes (see accompanying paper [1]). On the other hand, MinD dimerization and anchoring could be enhanced on pre-existing anionic phospholipid domains. We have tested MinD binding to model membranes in which acidic and zwitterionic phospholipids are either well-mixed or segregated to phase domains. The phase separation was achieved in binary mixtures of 1-Stearoyl-2-Oleoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol] (SOPG) with 1,2-Distearoyl-sn-Glycero-3-Phosphocholine (DSPC) or 1,2-Distearoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (DSPG) and binding to these membranes was compared with that to a fluid mixture of SOPG with 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (SOPC). The results demonstrate that MinD binding to the membrane is enhanced by segregation of anionic phospholipids to fluid domains in a gel-phase environment and, moreover, the protein stabilizes such domains. This suggests that an uneven binding of MinD to the heterogeneous native membrane is possible, leading to formation of a lipid-specific distribution pattern of MinD and/or modulation of its temporal behavior.     

Bacterial cell division: a moving MinE sweeper boggles the MinD

Placement of the division site in Escherichia coli is determined in part by three Min proteins. Recent studies have shown that MinE, previously thought to form a static ring near the division site at the midcell position, actually joins MinC and MinD in their rapid oscillation between the cell poles.