Translational studies with turnip yellow mosaic virus RNAs isolated from major and minor virus particles

Biophysical Structural Chemistr

Functional expression of a mouse H-2Kb gene isolated from non-expressing teratocarcinoma cells.

Embryonal carcinoma cells do not express H-2 antigens or beta 2-microglobulin. Recent studies have suggested that the expression of these antigens is likely to be controlled at the level of transcription. To study the precise organization of the corresponding genes and their possible expression in adult mouse cells, we have isolated H-2-related genes from a genomic cosmid library constructed with PCC4-aza-RI from DNA of EC cells. Clones isolated from the library after stringent hybridization with an H-2 cDNA probe were tested for their ability to direct H-2 antigen synthesis after DNA-mediated gene transfer in a fibroblastic L cell. Four clones have been found to code for the major transplantation antigen H-2Kb. Structural analysis showed that these clones contained the same entire H-2Kb gene, identical to the corresponding gene isolated from differentiated C57Bl/10 cells. Furthermore, the present studies showed that this embryonal carcinoma gene was expressed and was functional when transfected into a differentiated cell

HUMAN GASTRIC LIPASE

Ninety percentofthe dietary lipids in humans are triglycerides which constitute the essential part of the 100g to 150g daily fat intake in industrialized countries. It was thoughtuntil recently that the hydrolysis of dietary triglycerides began in the intestinal lumen and was catalysed exclusively by pancreatic lipase. Studies on gastrointestinal lipolysis have underestimated several importantpoints, particularly the role of gastric lipolysis. It is now well established that Human Gastric Lipase (HGL), is the first lipolytic enzyme involved in dietary fat digestion. HGL originates entirely from the fundic mucosa. Nolipolytic activity was detected in the lingual, pharyngeal or oesophagus areas. Using immunocytolocalization techniques, cells producing HGLwereidentified as the chief cells of gastric fundic glands already known to biosynthesize pepsin. HGL was purified to electrophoretic homogeneity (MW = 50 kDa)from gastric juice. It is a glycoprotein with a glycan moiety amounting about 15 to 20 % ofthe total protein weight. The complete amino acid sequence of HGL,derived from cDNA sequence, shows 80 % homology with rat lingual lipase. No structural homology exists between human gastric lipase and pancreatic lipase, except the G-X-S-X-G sequence found in otherlipases andserine esterases. This sequence containsa serine analogousto the essential Ser- 152 in human pancreatic lipase. HGL contains one free sulfhydryl group whichis essential to the expressionoflipaseactivity. HGL hydrolyses short chain (tributyrin) and long chain (Intralipide) triacylglycerols at similar rates. HGL activity is very dependentupon the interfacial tension between triacylglycerol and water. In the presence of amphiphiles such as bile salts or alimentary proteins, the tributyrin-waterinterfacial tension decreases and HGLis activated. Thus HGLis capable of hydrolyzing triglyceride emulsionsin the presence ofbile salts concentration prevailing in the upper small intestine and in the presence of alimentary proteins. These observations could explain the high dietary lipid absorption observed underpancreatic lipase deficiency. In vitro studies showed that prehydrolysis by HGLofIntralipide emulsion enable it to be subsequently hydrolyzed by humanpancreatic lipase. Fatty acid liberated by HGL probablytriggerthe later action of pancreatic lipase by changing the interfacial tension

A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology

International audienc

In vivo aminoacylation and 'processing' of turnip yellow mosaic virus RNA in Xenopus laevis oocytes [29]

IT is now well established that several plant and animal virus RNAs possess a 'tRNA-like' structure, as they are recognised in vitro by many tRNA-specific enzymes. To approach the problem of the possible physiological significance of these structures for the development of the virus, it seemed important to determine whether they are also recognised in vivo. The most logical approach would have been to use plant protoplast systems to study the behaviour of viral genomes in the infected cells. However, because such systems are still difficult to control, we decided to use the oocyte system. We describe here how turnip yellow mosaic virus (TYMV) RNA, which can be aminoacylated in vitro by valine1, was microinjected into Xenopus laevis oocytes, incubated in the presence of 3H-valine and the RNA charged in vivo analysed. We conclude that TYMV RNA, the 3′ terminal sequence of which is -CC (refs 2, 3), is amino-acylated in vivo. This indicates that the viral RNA is recognised by the oocyte tRNA nucleotidyltransferase and valyl-tRNA synthetase. Furthermore, the TYMV Val-RNA recovered after the in vivo reaction is fragmented and migrates between 4S and 5S RNA markers. This implies that (an) RNase(s) split(s) the viral genome, liberating this tRNA-like structure. © 1978 Nature Publishing Group.SCOPUS: le.jinfo:eu-repo/semantics/publishe