Search

It has been shown that Escherichia coli cells with increased expression of the rpoE gene encoding [[sigma].sup.E] exhibit enhanced cell lysis in early stationary phase. Further analysis of the lysis phenomenon was performed using a transient expression system of the rpoE gene and by DNA microarray. The former analysis revealed a [[sigma].sup.E]-directed cell lysis, specific for early stationary phase but not for the exponential phase. The microarray analysis with RNAs from exponential and early stationary phase cells revealed that a large number of genes were up-or down-regulated when the rpoE gene was induced, and that several genes were induced in a phase-specific manner. The upregulated genes include many previously identified [[sigma].sup.E] regulon genes, suggesting that a large number of genes are under the control of [[sigma].sup.E] in this organism. These genes are involved in various cellular activities, including the cell envelope, cellular processes, regulatory functions, transport and translation. Genes that are presumably related to phase-specific cell lysis in E. coli are discussed.

Research has been conducted on Escherichia coli protein YibP involving amino acid sequences. The properties of the yibP disrupted mutant cells and subcellular localization of the YibP protein have been investigated and the results are reported.

HemK, a universally conserved protein of unknown function, has high amino acid similarity with DNA-(adenine-N6) methyl transferases (MTases). A certain mutation in hemK gene rescues the photosensitive phenotype of a ferrochelatase-deficient (hemH) mutant in Escherichia coli. A hemK knockout strain of E. coli not only suffered severe growth defects, but also showed a global shift in gene expression to anaerobic respiration, as determined by microarray analysis, and this shift may lead to the abrogation of photosensitivity by reducing the oxidative stress. Suppressor mutations that abrogated the growth defects of the hemK knockout strain were isolated and shown to be caused by a threonine to alanine change at codon 246 of polypeptide chain release factor (RF) 2, indicating that hemK plays a role in translational termination. Consistent with such a role, the hemK knockout strain showed an enhanced rate of read-through of nonsense codons and induction of transfer-mRNA-mediated tagging of proteins within the cell. By analysis of the methylation of RF1 and RF2 in vivo and in vitro, we showed that HemK methylates RF1 and RF2 in vitro within the tryptic fragment containing the conserved GGQ motif, and that hemK is required for the methylation within the same fragment of, at least, RF1 in vivo. This is an example of a protein MTase containing the DNA MTase motif and also a protein-(glutamine-N5) MTase.

A micromagnetic model is used to study the head remanence of a perpendicular tapered main pole head and also discuss single pole heads and shielded heads. The reduction in the throat height is found to have less effect on the reduction in the head remanence in the tapered head than in the conventional head and the pole tip remanence is reduced to value closer to that of the conventional structure.