Characteristics of five bacteriophages of yellow-pigmented enterobacteria

Four bacteriophages (C2, C2F, E3, and E16P) belonging to morphological group C3 and one belonging to morphological group A3 (E16B) were purified by deuterium oxide gradient centrifugation and cesium chloride gradient centrifugation. Morphological group C3 phages had a densityd=1.534–1.541 and group A3 phage (E16B) had a densityd=1.492 in CsCl. Phages of morphological group C3 isolated onEnterobacter sakazakii (C2, C2F) and onErwinia herbicola (E3, E16P) were compared withSalmonella newport phage 7-11 with respect to host-range, genome size, antigenic relatedness, and ultraviolet and heat susceptibility. Phages C2 and C2F could multiply inEnterobacter cloacae, E. sakazakii, Erwinia herbicola, E. rhapontici, andLevinea malonatica; whereas phages E3, E16P, and 7-11 could multiply on these same species and onEscherichia coli and severalSalmonella serotypes. Molecular weights of phage DNAs were determined to be 58×10⁶ (C2), 60×10⁶ (7-11), 67×10⁶ (E3), and 39×10⁶ (E16B).All studied phages of morphological group C3 (includingSalmonella newport phage 7-11) were neutralized by anti-phage C2 serum. Despite differences in neutralization kinetics and in ultraviolet and heat sensitivities, these phages of morphological group C3 constitute one phage species. Phage E16B (morphological group A3) had a host-range limited toEnterobacter cloacae, Erwinia herbicola, andE. rhapontici; it was antigenically unrelated to the preceding phage group C3, and showed ultraviolet and heat susceptibility close to that of coliphage T4.     

Serratia species isolated from plants

Using the selective caprylate-thallous agar medium, the presence ofSerratia species was systematically examined in 623 plant samples. A total of 167Serratia strains was isolated from these plant samples and identified to species and biogroups. Uniform and characteristicSerratia populations were found in figs and coconuts: (i)Serratia ficaria was recovered from most figs collected in California, Tunisia, and France; various biotypes ofS. marcescens also were found in figs; (ii) onlyS. marinorubra was recovered from coconuts bought on two continents. From plants other than figs and coconuts, representatives were isolated of all eightSerratia species we presently recognize—with a large preponderance ofS. liquefaciens andS. proteamaculans. These other plant samples fell into threeSerratia-prevalence groups: (i) vegetables-mushrooms-mosses-decaying plant material (53.8% of these samples were positive forSerratia); (ii) grasses (23.7% positive); and (iii) trees and shrubs-small plants (8.4% positive). PigmentedS. marcescens biotypes were rarely isolated from plants (except from figs). Of theS. marcescens biogroups most frequently encountered in nosocomial and iatrogenic infections of man, A3 and A4 were isolated from plants in this study, but A5/8 and TCT were not.     

Insulin release: Reconciliation of the receptor and metabolic hypotheses

Summary Nutrients which stimulate insulin secretion are currently thought to initiate the series of cellular events eventually leading to insulin release either by interacting with a stereospecific receptor system (the regulatory site hypothesis) or by acting as a fuel (the substrate site hypothesis) in the pancreaticB-cell. The latter hypothesis is supported by a number of observations indicating that the capacity of nutrients to stimulate insulin release is indeed highly dependent on their capacity to increase catabolic fluxes in isolated pancreatic islets. However, these observations do not rule out the existence of nutrient receptors in islet cells. For instance, a nonmetabolized analog of L-leucine stimulates insulin release by causing allosteric activation of glutamate dehydrogenase, which should be considered, therefore, as a receptor for certain amino acids. Likewise, the increase in glycolytic flux, which is associated with the process of glucose-stimulated insulin release, is attributable not solely to a mass action phenomenon but also to the activation of phosphofructokinase by fructose 2.6-bisphosphate. The biosynthesis of this activator may involve a glucose receptor system. The fact that certain nutrient secretagogues (e.g D-glucose and L-leucine) act in the B-cell both as substrates and enzyme activators permits reconciliation of the substrate site and regulatory site hypotheses for insulin release.     

Glutamine Synthetase in Oligodendrocytes and Astrocytes: New Biochemical and Immunocytochemical Evidence

The results of recent immunocytochemical experiments suggest that glutamine synthetase (GS) in the rat CNS may not be confined to astrocytes. In the present study, GS activity was assayed in oligodendrocytes isolated from bovine brain and in oligodendrocytes, astrocytes, and neurons isolated from rat forebrain, and the results were compared with new immunochemical data. Among the cells isolated from rat brain, astrocytes had the highest specific activities of GS, followed by oligodendrocytes. Oligodendrocytes isolated from white matter of bovine brain had GS specific activities almost fivefold higher than those in white matter homogenates. Immunocytochemical staining also showed the presence of GS in both oligodendrocytes and astrocytes in bovine forebrain, in three white-matter regions of rat brain, and in Vibratome sections as well as paraffin sections.     

C32 human melanoma cell endogenous lectins: characterization and implication in vesicle-mediated melanin transfer to keratinocytes.

To optimize skin pigmentation in order to help body prevention against UV radiation, the mechanism of melanin pigment transfer from melanocytes to keratinocytes must be elucidated. Melanin transfer to keratinocytes requires specific recognition between keratinocytes and melanocytes or melanosomes. Cell surface sugar-specific receptor (membrane lectin) expression was studied in human C32 melanoma cells, an amelanotic melanoma, by flow cytometry analysis of neoglycoprotein binding as an approach to the molecular specificity. Sugar receptors on melanocytes are mainly specific for alpha-L-fucose. Their expression is enhanced upon treatment by the diacylglycerol analogue 1-oleoyl-2-acetylglycerol, which can induce melanin synthesis in amelanotic human melanoma cells in a dose-dependent manner. Flow cytometry analyses showed a small-sized population of vesicles distinguishable from large cells by their fluorescence properties upon neoglycoprotein binding. Sorting indicated that the small-sized subpopulation is composed of vesicles produced by melanocytic cells. Upon vesicle formation, a selective concentration of sugar receptors specific for 6-phospho-beta-D-galactosides appears in the resulting melanocytic vesicles. Vesicles are recognized and taken up by cultured keratinocytes and a partial inhibitory effect was obtained upon cell incubation in the presence of neoglycoproteins, indicating a possible participation of sugar receptors in this recognition. The validity for such a model to help in understanding the natural melanin transfer by melanosomes is confirmed by electron microscopy, which demonstrates the presence of melanin inside keratinocytic cells upon incubation with melanocytic vesicles.     

Nuclear localization of two steroid receptor-associated proteins, hsp90 and p59

It has been proposed that the unliganded nontransformed form of steroid hormone receptor is a heterooligomer comprising, in addition to the hormone-binding subunit, two associated proteins: a heat shock protein of MW 90,000 (hsp90) and another protein of MW 59,000 (p59). Using monoclonal antibodies, we demonstrate immunocytochemically the presence of both hsp90 and p59 in cell nuclei of progesterone target cells of the rabbit uterus. While steroid receptors (e.g., progesterone receptors) appear to be exclusively nuclear, we find p59 predominantly in the cell nuclei and hsp90 in both the nucleus and the cytoplasm. In addition, Western blotting of high-salt extracts of nuclear proteins detects the presence of hsp90 and p59 in the nuclei of rabbit uterus. These observations are consistent with the presence of the untransformed heterooligomeric form of steroid hormone receptors in the nuclei of target cells.     

Biochemical characterization ofSerratia liquefaciens sensu stricto,Serratia proteamaculans,andSerratia grimesii sp. nov.

Seven biochemical groups were found among strains previously labeledSerratia liquefaciens (groups C1ab, C1c, C1d, EB, RB, RQ, and Adc). Comparison of biochemical data with DNA relatedness data allowed the definition (or redefinition) of threeSerratia species:Serratia liquefaciens sensu stricto (group C1ab),Serratia proteamaculans (groups C1c, EB, RB, and RQ), andSerratia grimesii sp. nov. (groups C1d and Adc). Biochemical group RQ, which is genomically related toS. proteamaculans at the borderline of species level, is proposed as a new subspecies ofS. proteamaculans (Serratia proteamaculans subsp.quinovora). Group Adc (3 strains) is also ambiguously related toS. grimesii, but no other proposal is made pending additional studies. The type strains of the newly named taxa,S. grimesii andS. proteamaculans subsp.quinovora, are respectively ATCC 14460 and strain 4364 (= CIP 8195 = ATCC 33765).     

Clusters of repeated sequences of chicken DNA are extensively methylated but contain specific undermethylated regions

In the chicken genome there are middle repetitive DNA sequences with a clustered organization. Each cluster is composed of members of different families of repeated DNA sequences and usually contains only one member of each family. Many clusters have the same assortment of repeated sequences but they are in scrambled order from cluster to cluster. These clusters usually exceed 20 × 10³ bases in length and comprise at least 10% of the repeated DNA of the chicken. The repeated sequences that are cluster components are extensively methylated. Methylation was detected by comparing HpaII and MspI digests of total DNA, where the occurrence of the sequence C-m⁵C-G-G is indicated when HpaII (cleaves C-C-G-G) fragments are larger than those generated by MspI (cleaves C-m⁵C-G-G or C-C-G-G). In hybridization experiments with Southern (1975) blots of total DNA digested with either HpaII or MspI, the cloned probes representing clustered repeated sequences showed a dramatic difference in the lengths of restriction fragments detected in the two digests. Many of the sequences that comprise these clusters are methylated in most of their genomic occurrences. There are patterns of methylation that are reproduced faithfully from copy to copy. The overall distribution of methylation within clusters seems to be regional, with long methylated DNA segments interrupted by specific undermethylated regions.