On the rotational brownian motion of a bacterial idle motor. II. Theory of fluorescence correlation spectroscopy

The photon flux autocorrelation function of a fluorescent label attached to a bacterial motor shaft is calculated for the case in which the bacterial motor is considered to be actively but idly rotating. It is shown that even when the fluorescent label has a very short lifetime, fluorescence correlation spectroscopy should provide a useful tool for determining the rate of revolution of the bacterial motor under various solution conditions.     

Characterization of translucent segments observed in an smbA mutant of Escherichia coli

Abstract The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22°C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrastt microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22°C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.     

Posttranslational modification and microtubule stability

We have probed the relationship between tubulin posttranslational modification and microtubule stability, using a variation of the antibody-blocking technique. In human retinoblastoma cells we find that acetylated and detyrosinated microtubules represent congruent subsets of the cells' total microtubules. We also find that stable microtubules defined as those that had not undergone polymerization within 1 h after injection of biotin-tubulin were all posttranslationally modified; furthermore dynamic microtubules were all unmodified. We therefore conclude that in these cells the stable, acetylated, and detyrosinated microtubules represent the same subset of the cells' total network. Posttranslational modification, however, is not a prerequisite for microtubule stability and vice versa. Potorous tridactylis kidney cells have no detectable acetylated microtubules but do have a sizable subset of stable ones, and chick embryo fibroblast cells are extensively modified but have few stable microtubules. We conclude that different cell types can create specific microtubule subsets by modulating the relative rates of posttranslational modification and microtubule turnover.     

Methylation strongly enhances DNA bending in the replication origin region of the Escherichia coli chromosome

Summary Two-dimensional gel electrophoresis, at high and low temperatures, and gel mobilities of circularly permuted DNA segments showed a large bending locus about 50 bp downstream from the right border of the 245 by oriC box, a minimal essential region of autonomous replication on the Escherichia coli chromosome. Bending was strongly enhanced by Dam methylation. In DNA from a Dam^– strain, the mobility anomaly arising from altered conformation was much reduced, but was raised to the original level by methylation in vivo or in vitro. Enhancement of the mobility anomaly was also observed by hybrid formation of the Dam^– strand with the Dam⁺ strand. Near the bending center, GATC, the target of Dam methylase, occurs seven times arranged essentially on the same face of the helix with 10.5 by per turn. We concluded that small bends at each Dam site added up to the large bending detectable by gel electrophoresis.     

The occurrence of a premature form of egg-specific protein in vitellogenic follicles ofBombyx mori

Summary Analysis of yolk proteins of the silkworm,Bombyx mori, by SDS-polyacrylamide gel electrophoresis and immunoblotting showed that there was a developmental change in subunit composition of egg-specific protein; egg-specific protein consisting of 72 kDa subunits alone (premature form) was found in vitellogenic follicles, whereas the protein in mature eggs was composed of 72 kDa and 64 kDa subunits (mature form). The premature form of egg-specific protein was purified from young ovaries to homogeneity using a high performance liquid chromatography system. The purified protein had an apparent molecular mass of 225 kDa which could not be distinguished from that of the mature form. By circular dichroism analysis, both egg-specific proteins were estimated to have about 30% -helix and 20% -sheet, but the mature form showed a relatively rigid conformation in the aromatic region. The premature egg-specific protein purified from vitellogenic ovaries, consisted of three 72 kDa subunits, whereas mature egg-specific protein was composed of two 72 kDa subunits and one 64 kDa subunit. All of these subunits showed the same immunoreactivity towards antiserum raised against the mature form. An identical NH₂-terminal amino acid sequence was found in both 72 kDa polypeptides and 64 kDa polypeptide for the initial 10 amino acids.Abbreviations SDS sodium dodecyl sulfate - PMSF phenylmethylsulfonyl fluoride - PAGE polyacrylamide gel electrophoresis - HPLC high performance liquid chromatography - ESP egg-specific protein - Vtn vitellin     

Immunocytochemical observation of paraquat-induced alveolitis with special reference to class II MHC antigens.

The expression of class II major histocompatibility complex (MHC) antigens on alveolar epithelial cells and macrophages was investigated immunocytochemically in paraquat-induced alveolitis in the rat lung. Until 2 days after paraquat injection, class II MHC antigens were expressed on the type II alveolar epithelium without any inflammatory cellular infiltration. From the 4th to the 7th day after paraquat injection, class II MHC antigen-positive macrophages increased in the alveolar spaces, whereas the expression on the type II alveolar epithelium became obscure. Over 10 days after the injection, interstitial fibrosis progressed and the intra-alveolar inflammatory infiltrates decreased. Epithelial cells lining the thickened fibrous septa no longer expressed class II MHC antigens. These results suggest that chemical stimuli can induce class II MHC antigen expression on the type II alveolar epithelium in the early stage of cellular injury, followed by inflammatory infiltration and interstitial fibrosis.