Actin-independent behavior and membrane deformation exhibited by the four-transmembrane protein M6a

M6a is a four-transmembrane protein that is abundantly expressed in the nervous system. Previous studies have shown that over-expression of this protein induces various cellular protrusions, such as neurites, filopodia, and dendritic spines. In this detailed characterization of M6a-induced structures, we found their varied and peculiar characteristics. Notably, the M6a-induced protrusions were mostly devoid of actin filaments or microtubules and exhibited free random vibrating motion. Moreover, when an antibody bound to M6a, the membrane-wrapped protrusions were suddenly disrupted, leading to perturbation of the surrounding membrane dynamics involving phosphoinositide signaling. During single-molecule analysis, M6a exhibited cytoskeleton-independent movement and became selectively entrapped along the cell perimeter in an actin-independent manner. These observations highlight the unusual characteristics of M6a, which may have a significant yet unappreciated role in biological systems.     

Distribution pattern of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in a reservoir

Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased.     

Association of a regulatory gene, slyA with a mouse virulence of Salmonella serovar Choleraesuis

The influence of slyA gene, originally found in Salmonella serovar Typhimurium as a regulatory gene for the expression of virulence genes, on a mouse virulence of S. serovar Choleraesuis was investigated by using an slyA-defective mutant. The defective mutant was constructed by the insertion of a kanamycin-resistance gene (aph) into the cloned slyA gene, and the homologous recombination with the intact slyA gene on the chromosome. The mutant strain showed the LD50 value for BALB/c mouse approximately 10(5) higher than that of the parent strain. The increase of the LD50 value was the same order as that shown by the mutation of the slyA gene of S. serovar Typhimurium, although LD50 of the wild-type strain of S. serovar Choleraesuis was 40-fold higher than that of S. serovar Typhimurium. The time course of infection observed in the mice organs also proved the clear difference of the virulence between the parent and the mutant strains. These results suggested that the slyA gene product functions as a virulence-associated regulator also in S. serovar Choleraesuis.     

Crystal structure of archaeal toxin-antitoxin RelE-RelB complex with implications for toxin activity and antitoxin effects

The Escherichia coli chromosome encodes toxin-antitoxin pairs. The toxin RelE cleaves mRNA positioned at the A-site in ribosomes, whereas the antitoxin RelB relieves the effect of RelE. The hyperthermophilic archaeon Pyrococcus horikoshii OT3 has the archaeal homologs aRelE and aRelB. Here we report the crystal structure of aRelE in complex with aRelB determined at a resolution of 2.3 A. aRelE folds into an alpha/beta structure, whereas aRelB lacks a distinct hydrophobic core and extensively wraps around the molecular surface of aRelE. Neither component shows structural homology to known ribonucleases or their inhibitors. Site-directed mutagenesis suggests that Arg85, in the C-terminal region, is strongly involved in the functional activity of aRelE, whereas Arg40, Leu48, Arg58 and Arg65 play a modest role in the toxin's activity.