A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans

The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities.     

Phenotypic Characterization of Adenovirus Type 12 Temperature-Sensitive Mutants in Productive Infection and Transformation

Eleven temperature-sensitive mutants of adenovirus type 12, capable of forming plaques in human cells at 33 C but not at 39.5 C, were isolated from a stock of a wild-type strain after treatment with either nitrous acid or hydroxyl-amine. Complementation tests in doubly infected human cells permitted a tentative assignment of eight of these mutants to six complementation groups. Temperature-shift experiments revealed that one mutant is affected early and most of the other mutants are affected late. Only the early mutant, H12ts505, was temperature sensitive in viral DNA replication. Infectious virions of all the mutants except H12ts505 and two of the late mutants produced at 33 C, appeared to be more heat labile than those of the wild type. Only H12ts505 was temperature sensitive for the establishment of transformation of rat 3Y1 cells. One of the late mutants (H12ts504) had an increased transforming ability at the permissive temperature. Results of temperature-shift transformation experiments suggest that a viral function affected in H12ts505 is required for “initiation” of transformation. Some of the growth properties of H12ts505-transformed cells were also temperature dependent, suggesting that a functional expression of a gene mutated in H12ts505 is required to maintain at least some aspects of the transformed state.     

Aggregatibacter actinomycetemcomitans induces detachment and death of human gingival epithelial cells and fibroblasts via elastase release following leukotoxin‐dependent neutrophil lysis

Aggregatibacter actinomycetemcomitans is considered to be associated with periodontitis. Leukotoxin (LtxA), which destroys leukocytes in humans, is one of this bacterium's major virulence factors. Amounts of neutrophil elastase (NE), which is normally localized in the cytoplasm of neutrophils, are reportedly increased in the saliva of patients with periodontitis. However, the mechanism by which NE is released from human neutrophils and the role of NE in periodontitis is unclear. In the present study, it was hypothesized that LtxA induces NE release from human neutrophils, which subsequently causes the breakdown of periodontal tissues. LtxA‐treatment did not induce significant cytotoxicity against human gingival epithelial cells (HGECs) or human gingival fibroblasts (HGFs). However, it did induce significant cytotoxicity against human neutrophils, leading to NE release. Furthermore, NE and the supernatant from LtxA‐treated human neutrophils induced detachment and death of HGECs and HGFs, these effects being inhibited by administration of an NE inhibitor, sivelestat. The present results suggest that LtxA mediates human neutrophil lysis and induces the subsequent release of NE, which eventually results in detachment and death of HGECs and HGFs. Thus, LtxA‐induced release of NE could cause breakdown of periodontal tissue and thereby exacerbate periodontitis.     

Day-night changes in production of carbohydrate and protein by natural phytoplankton population from Lake Biwa, Japan

The ¹³C and gas chromatography-mass spectrometry (¹³C-GC-MS)method was applied to determine the day-night changes in thecomposition of photosynthetic products of the natural phytoplanktonpopulation from Lake Biwa, Japan. Glucose is the most abundantmonosaccharide in acid-hydrolyzable carbohydrate. The contributionof glucose was high in incubatesd samples in daytime and decreasedduring the night. Other monosaccharides (rhamnose, fucose, ribose,arabinose, xylose, mannose and galactose) and amino acids tendedto be produced throughout both day- and night-time. These resultssuggested that the carbon flows from glucose, which might constitutereserve glucan, to other monosaccharides and amino acids duringnight-time. The disproportionate production of glucose (reservedglucan) during daytime was thus partly cancelled out at night.     

Regulated Expression of a Gene-Fusion Product Derived from the Gene for Phytochrome I from Pisum sativum and the uidA Gene from E. coli in Transgenic Petunia hybrida

The 5'-upstream region (2.4 kb) of the gene for phytochromeI from Pisum sativum (phyl) was fused to the uidA gene fromEscherichia coli that encodes ß-glucuronidase (GUS).The resulting PHY-GUS fusion was introduced into Petunia hybridaand was used as a reporter of the expression of the phyI genewhich was recognized by GUS activity. The PHY-GUS fusion wasexpressed at a relatively high level when transgenic plantswere grown in the dark, while leaves and stems of light-grownplants showed background activity. Flowers of light-grown plantswere shown to have significant levels of GUS activity but rootsdid not have such activity. When light-grown transgenic plantswere transferred to the dark, they expressed the activity atlevels that corresponded to those of dark-grown plants. Lighttreatment prior to growth in darkness revealed red/far-red reversibilityof recovery of the activity. Thus, the 2.4-kb fragment fromthe 5' region of the phyI gene carries the information necessaryfor the light-repressible autoregulation. (Received March 30, 1991; Accepted May 20, 1991)     

A photosystem other than PS370 also mediates the negative phototaxis of Halobacterium halobium

Abstract It was found that a photorepellent system other than photosystem 370 (PS370) also controls the behavior of Halobacterium halobium . Both the dependence of background illumination and wavelength where the response showed maximum action distinguished that photosystem from PS370 whose photoreceptor pigment is thought to be an intermediate of s-rhodopsin (sR). A mutant strain that has no detectable activity in PS370 and in photoattractant response was isolated. This mutant strain showed the repellent response due to the new photosystem.     

Purification and properties of rat brain dipeptidyl aminopeptidase

Dipeptidyl aminopeptidase, which hydrolyzes the 7-(Gly-Pro)-4-methylcoumarinamide, has been purified from the brains of 3 week-old rats. It was purified about 2,600-fold by column chromatography on CM-cellulose, hydroxyapatite and Gly-Pro AH-Sepharose. This enzyme hydrolyzed Lys-Ala-beta-naphthylamide well with an optimum pH of 5.5. It was inhibited by diisopropyl fluorophosphate, phenyl-methanesulfonyl fluoride, some cations, and puromycin, but was not inhibited by p-chloromercuribenzoate, N-ethylmaleimide, dithiothreitol, EDTA, iodoacetic acid, and bacitracin, indicating that rat brain dipeptidyl aminopeptidase is a serine protease. This enzyme showed a molecular weight of 220,000 by gel filtration and of 51,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The properties of purified rat brain dipeptidyl aminopeptidase were similar to those of bovine pituitary dipeptidyl peptidase II, but the molecular weight and substrate specificity of these enzymes were different.     

Growth Regulation in Dwarf Barley Coleoptiles by the Minor Cell Wall Components, Galactose and Mannose

Sugar compositions of cell walls of dark-grown coleoptiles from12 barley strains, 11 of which were coleoptilar semi-dwarf strains,were analyzed on days 2 and 3 after germination. Major wallcomponents of the 12 strains were arabinose, xylose, and glucosein hemicellulose and cellulose; minor components were galactoseand mannose. The sugar content of each wall component per unit length wasnot correlated to any growth parameters calculated from a logisticequation simulating coleoptile growth, but the relative contentsof galactose and mannose in relation to the total wall sugarcontent was correlated to the growth rate on day 3 and the growthcontinuing period. These facts suggest that growth of these12 barley strains in the late growth stage is regulated by theminor wall components, galactose and mannose. ¹ Dedicated to the late Professor Joji Ashida. (Received October 12, 1982; Accepted January 12, 1983)