Three-dimensional structure of physalis mottle virus: implications for the viral assembly.

The structure of the T=3 single stranded RNA tymovirus, physalis mottle virus (PhMV), has been determined to 3.8 A resolution. PhMV crystals belong to the rhombohedral space group R 3, with one icosahedral particle in the unit cell leading to 20-fold non-crystallographic redundancy. Polyalanine coordinates of the related turnip yellow mosaic virus (TYMV) with which PhMV coat protein shares 32 % amino acid sequence identity were used for obtaining the initial phases. Extensive phase refinement by real space molecular replacement density averaging resulted in an electron density map that revealed density for most of the side-chains and for the 17 residues ordered in PhMV, but not seen in TYMV, at the N terminus of the A subunits. The core secondary and tertiary structures of the subunits have a topology consistent with the capsid proteins of other T=3 plant viruses. The N-terminal arms of the A subunits, which constitute 12 pentamers at the icosahedral 5-fold axes, have a conformation very different from the conformations observed in B and C subunits that constitute hexameric capsomers with near 6-fold symmetry at the icosahedral 3-fold axes. An analysis of the interfacial contacts between protein subunits indicates that the hexamers are held more strongly than pentamers and hexamer-hexamer contacts are more extensive than pentamer-hexamer contacts. These observations suggest a plausible mechanism for the formation of empty capsids, which might be initiated by a change in the conformation of the N-terminal arm of the A subunits. The structure also provides insights into immunological and mutagenesis results. Comparison of PhMV with the sobemovirus, sesbania mosaic virus reveals striking similarities in the overall tertiary fold of the coat protein although the capsid morphologies of these two viruses are very different.     

Expression of the Epstein-Barr virus gp350/220 gene in rodent and primate cells.

The gene encoding the Epstein-Barr virus envelope glycoproteins gp350 and gp220 was inserted downstream of the cytomegalovirus immediate-early, Moloney murine leukemia virus, mouse mammary tumor virus, or varicella-zoster virus gpI promoters in vectors containing selectable markers. Host cell and recombinant vector systems were defined which enabled the isolation of rodent or primate cell clones which expressed gp350/220 in substantial quantities. Continued expression of gp350/220 required maintenance of cells under positive selection for linked markers and periodic cloning. gp350/220 expressed in various host cells varied slightly in electrophoretic mobility, probably reflecting differences in glycosylation. Insertion of a stop codon into the gp350/220 open reading frame, upstream of the putative membrane anchor sequence, resulted in efficient secretion of truncated gp350 and gp220 from rat pituitary (GH3) cells. gp350/220 expressed in mammalian cells is highly immunogenic and elicits virus-neutralizing antibodies when administered to mice.     

Interspecific variations in the surface ultrastructure of the gills of freshwater mullets

SEM studies were made on the gills of freshwater mullets,Rhinomugil corsula andSicamugil cascasia, to correlate surface ultrastructure of various gill units with their probable functions. Two types of lamellated gill rakers of the former fish are suited for plankton feeding and the short, stumpy and transversely beaded gill rakers of the latter reflect the varied food and feeding habit of the fish.R. corsula has numerous mucous glands on the epithelium covering the gill arch and gill filaments,S. cascasia has fewer. In accordance with the differences in the density and distribution of the mucous glands, the microridged epithelial cells also show variations in their architectural plan. In both species the epithelium of the secondary lamellae is smooth, probably an adaptation for better gaseous exchange.     

Histochemical localization of acid mucopolysaccharide in the respiratory muscles of a fresh-water air-breathing siluroid fish, Clarias batrachus (Linn.).

Respiratory muscles involved in gill ventilation (= irrigation) of an amphibious siluroid fish, Clarias batrachus (Linn.) were studied by phase contrast and light microscopy after the treatment with PAS. Alcian Blue at pH 2.5 and 1.0, dialyzed iron and Toludine Blue. The transverse muscle bands lightly stained with PAS, Alcian Blue at pH 2.5 and 1.0 and Dialyzed Iron suggesting that the mucopolysaccharide occured in relatively low concentrations. Phase contrast microscopy indicated that the transverse bands stained by the above mentioned reagents correspond to the I-bands. Methylation for 4 hours at 60 degrees C prevented I-band staining with Alcian Blue in the muscles studied. Saponification alone left I-band alcianophilia intact. These findings reveal that myofibrillar I-bands of respiratory muscles contain sulphated acid mucosubstances.     

Morphometries of the respiratory organs of the Indian green snake-headed fish, Channa punctata

Measurements of the dimensions of the different gills and the suprabranchial chambers have been made and the data analysed with respect to body weight using logarithmic transformations (Y = aW^b). The slope (b) for area of the total gill surface is 0–592 and for the supra-branchial chamber 0–696, and their combined respiratory surface: 0–623. The slope values for the surface areas of the 1st, 2nd, 3rd and the 4th gill arches were 0–595,0–578,0–614 and 0–572 respectively.
The slope for secondary lamellae/mm is –0138 and that for the bilateral surface area of an average-sized lamella 0–304.
These results indicate differences in growth patterns for the dimensions of the different gills. The growth-related decrease in the number of secondary lamellae/mm and size of an average secondary lamella together with evidence from "drowning" experiments and diffusing capacity calculation, suggest that this fish is better adapted for aquatic respiration than Anabas or Saccobranchus. The slopes for the total respiratory surface area and gill area seem to be comparatively low in this species.     

The effect of relaxed functional constraints on the photosynthetic gene rbcL in photosynthetic and nonphotosynthetic parasitic plants

The photosynthetic gene rbcL has been lost or dramatically altered in some lineages of nonphotosynthetic parasitic plants, but the dynamics of these events following loss of photosynthesis and whether rbcL has sustained functionally significant changes in photosynthetic parasitic plants are unknown. To assess the changes to rbcL associated with the loss of functional constraints for photosynthesis, nucleotide sequences from nonparasitic and parasitic plants of Scrophulariales were used for phylogeny reconstruction and character analysis. Plants in this group display a broad range of parasitic abilities, from photosynthetic ("hemiparasites") to nonphotosynthetic ("holoparasites"). With the exception of Conopholis (Orobanchaceae), the rbcL locus is present in all parasitic plants of Scrophulariales examined. Several holoparasitic genera included in this study, including Boschniakia, Epifagus, Orobanche, and Hyobanche, have rbcL pseudogenes. However, the holoparasites Alectra orobanchoides, Harveya capensis, Harveya purpurea, Lathraea clandestina, Orobanche corymbosa, O. fasciculata, and Striga gesnerioides have intact open reading frames (ORFs) for the rbcL gene. Phylogenetic hypotheses based on rbcL are largely in agreement with those based on sequences of the nonphotosynthetic genes rps2 and matK and show a single origin of parasitism, and loss of photosynthesis and pseudogene formation have been independently derived several times in Scrophulariales. The mutations in rbcL in nonparasitic and hemiparasitic plants would result in largely conservative amino acid substitutions, supporting the hypothesis that functional proteins can experience only a limited range of changes, even in minimally photosynthetic plants. In contrast, ORFs in some holoparasites had many previously unobserved missense substitutions at functionally important amino acid residues, suggesting that rbcL genes in these plants have evolved under relaxed or altered functional constraints.      

Cytology of recurrent ameloblastoma with malignant change. A case report

BACKGROUND: Ameloblastoma is a rare tumor of the jaw that arises from the odontogenic epithelium. Ameloblastomas have a propensity for local recurrence and, rarely, for metastasis. The term malignant ameloblastoma is reserved for those metastasizing tumors that retain the typical morphology of ameloblastoma. Fine needle aspiration (FNA) reports on ameloblastomas are scant, and those on malignant ameloblastomas are still more so. CASE: In a case of malignant ameloblastoma diagnosed by FNA cytology, the clinical presentation was that of a malignant neoplasm. FNA smears were highly cellular and showed isolated, scattered cells and small groups of basaloid cells and polygonal squamous epithelial cells. Stellate and spindle-shaped cells were also seen in the background. The cytologic diagnosis was subsequently confirmed on histopathology. CONCLUSION: The characteristic combination of cells in FNA smears facilitated the diagnosis of ameloblastoma. Since the biologic behavior of the tumor was that of a malignant neoplasm, the slides were reviewed. The cytologic smears did not exhibit sufficient features of malignancy to label the lesion malignant.     

Integrin-dependent tyrosine phosphorylation and growth regulation by Vav

The proto-oncogene product p95Vav (Vav) undergoes rapid phosphorylation on tyrosine following stimulation of the T or B cell antigen receptor, and in response to a variety of other cell surface stimuli. Vav contains, among other, a guanine nucleotide exchange factor domain with homology to the Rho/Rac/CDC42 exchange protein Db1. It has been recently shown that Vav is functionally linked to small GTPases of the Rho family, suggesting that it is an activator of Rho GTPases and may participate in regulation of cytoskeletal organization. The present study shows that cell adhesion to fibronectin triggers rapid phosphorylation of Vav on tyrosine in Vav-transfected CHO cells and in Jurkat T cells. Vav phosphorylation is strongly dependent on adhesion and is mediated by beta 1 integrins. Furthermore, Vav overexpression enhances the adhesion-dependent increase in the rate and extent of phosphorylation on focal adhesion kinase and paxillin, and the formation of stress fibers and lamellipodia. In addition, there is a marked increase in the amount of Vav localized to the triton-insoluble fraction following 1 h of incubation on FN. Finally, Vav increases the growth rate of the cells in an adhesion-dependent manner. Our results strongly implicate Vav as a mediator of integrin signal transduction.     

Potential pathogenic factors produced by a clinical nontoxigenicVibrio cholerae O1

A clinical isolate of nontoxigenicVibrio cholerae O1 that caused intestinal fluid accumulation (FA) in adult mice produced proteolytic, hemolytic, and cytotoxic activities in in vitro assays. The linkage of these secreted factors to the FA activity was studied by transposon (TnphoA) mutagenesis. Ten of the 12 TnphoA insertion mutants that were defective for proteolytic activity produced FA, hemolytic and cytotoxic activities; the remaining two mutants lost these latter three activities. These results indicate that FA activity is independent of proteolytic activity but closely associated with cytotoxic and hemolytic activities. Our results with the adult mouse model and a nontoxigenicV. cholerae O1 are in general agreement with previous studies that demonstrated linkage of cytotoxin and hemolysin of toxigenicV. cholerae O1 and non-O1 with FA activity in rabbit ileal loops.