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E Webb

Publications and source records attributed to E Webb.

86 records · Page 5Linked to original sources
PubMed1976

General and specific effects of amino acid starvation on the formation of undermodified Escherichia coli phenylalanine tRNA.

The heterogeneity of undermodified phenylalanine tRNA produced in relaxed control E. coli during amino acid starvation was investigated. Examination of the RPC-5 elution profiles of tRNAPhe prepared from non-starved cells and cells starved of a variety of amino acids, including some known to be involved in the formation of modified bases revealed that: (1) only one species of fully modified tRNAPhe appears to occur in cells grown in enriched medium; (2) at least two chromatographically unique isoacceptor species are observed in addition to the normal tRNAPhe in starved cells; (3) the unique, undermodified species of tRNAPhe from leucine-starved cells, known to be deficient in dihydrouridine, pseudouridine, 2-thiomethyl-N6-(delta2-isopentenyl) adenosine and 3-(3-amino-3-carboxypropyl) uridine, co-elute with the unique species produced in cells starved of histidine or arginine or treated with puromycin or chloramphenicol; (4) additional unique species of tRNAPhe can be detected in methyl- and sulfur-deficient tRNA from methionine- and cysteine-starved cells; (5) analysis of phenoxyacetylated tRNA revealed that the chromatographically unique and normal species from starved cells contain subspecies deficient in 3-(3-amino-3-carboxypropyl) uridine; and (6) using phenoxyacetylation as a means of effecting the resolution of undermodified subspecies, a total of at least ten chromatographically unique subspecies of rRNAPhe were detected in an organism that appears to posses only one gene for tRNAPhe. Taken together, the results support the view that there are both general and specific effects of amino acid starvation on the post-transcriptional modification of tRNA.

Amino Acids↗
PubMed1976

Unique phenylalanine transfer ribonucleic acids in relaxed control Escherichia coli: genetic origin and some functional properties.

Inhibition of protein synthesis in relaxed control E. coli results in the formation of chromatographically unique isoacceptor species of phenylalanine tRNA. The genetic origin and some functional properties of the major unique species of tRNA (Phe) produced during leucine starvation were investigated. RNA:DNA hybridization analyses revealed that the normally occurring and major unique species of tRNA (Phe) are generated from DNA sequences which are identical or closely related and that there may be only one such sequence in the E. coli chromosome. Results from 32P pulse-chase experiments revealed that the unique tRNA (Phe) can be converted to a chromatographically normal form upon resumption of cell growth in fully supplemented medium. These findings, taken with earlier results which indicate that the unique species is not derived from preexisting, normally occurring species, indicate that the unique tRNA(Phe) is a modification-deficient form of the normal species. Comparative studies of the unique and normal phenylalanine tRNAs revealed that the unique species is aminoacylated at a much lower rate than the normal species and is only about 60% as efficient in a tRNA-dependent, poly(U)-directed protein synthesizing system.

Binding Sites↗
PubMed1975

Fractionation and characterization of surface antigens from group A Neisseria meningitidis.

Group A meningococcal surface components were first subjected to fractionation with a mixture of chloroform-methanol. Sodium dodecyl sulfate-acrylamide gel electrophoresis of the aqueous phase containing 30 to 40% of the original material revealed only two polypeptide components and a slowly migrating carbohydrate component. The soluble fraction of the interphase was found to contain most of the bacterial surface proteins and the chloroform-methanol phase essentially all of the lipid components. The components of the aqueous phase were further fractionated by use of the hydrophobic affinity column, 4-phenylbutylamino-Sepharose and gradient elution with NaCl to yield fractions I and II. Fraction II was further separated into a minor and a major component (IIb) with Sepharose G-200. Fraction I contained the group A polysaccharide in ionic linkages with a minor polypeptide component (6%). It elicited bactericidal antibodies in rabbits and protected mice against homologous challenge, whereas the polysaccharide alone was non-immunogenic in these animals. Fraction IIb was a polysaccharide-polypeptide complex with unknown linkages; it induced a low concentration of rabbit antibodies that were bactericidal to group A and C meningococci. Mice vaccinated with fraction IIb were most resistant to homologous challenge and the resistance was also extended to challenges with group B and C cells. Fractions I and IIb appeared to be useful alternatives to the currently employed group-specific polysaccharide vaccines for the protection against drug-resistant meningococci. A simplified procedure for the preparation of group-specific polysaccharide was presented.

Amino Acids↗
PubMedDate not supplied

Variant (6 ; 15) translocation in a murine plasmacytoma occurs near an immunoglobulin kappa gene but far from the myc oncogene.

Chromosome translocations in B-lymphoid tumours are providing intriguing insights and puzzles regarding the role of immunoglobulin genes in the activation of the myc oncogene (reviewed in refs 1, 2). The 15 ; 12 translocations found in most murine plasmacytomas and the analogous 8 ; 14 translocation in human Burkitt's lymphomas involve scissions of murine chromosome 15 (human chromosome 8) near the 5' end of the c-myc gene and subsequent fusion near an immunoglobulin heavy-chain gene. The less well characterized 'variant' translocations found in about 15% of such tumours also involve the myc-bearing chromosome band, but exchange occurs with a chromosome bearing an immunoglobulin light-chain locus--in mice, the kappa-chain locus bearing chromosome 6 (refs 3-5) and, in man, chromosome 2 (or 22), at the same band at which the kappa (or lambda) locus lies (reviewed in ref. 1). The Burkitt variant translocations involve scissions 3' of c-myc; one 8 ; 22 translocation placed the C lambda locus just 3' of c-myc, but usually the chromosome 8 breakpoint is a greater, but unknown, distance away from c-myc, more than 20 kilobases (kb) in one 8 ; 2 translocation involving the C kappa gene. Little is known about the murine 6 ; 15 translocations, although a C kappa gene cloned from one plasmacytoma (PC7183) is linked, via chromosome 12 sequences, to an unidentified region of chromosome 15 (ref. 11). We describe here the chromosome fusion region from plasmacytoma ABPC4, which displays the typical reciprocal 6;15 translocations. We find that the chromosome 6 breakpoint is near C kappa but, unlike those in the heavy-chain locus, not at a position where immunoglobulin genes normally recombine. Moreover, the chromosome 15 sequences involved in the ABPC4 translocation are not derived from the vicinity of c-myc.

Animals↗
PubMedDate not supplied

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Humans↗