LYS70 of E. coli Quinolinate Phosphoribosyltransferase Is Protected from Chemical Modification by Formation of an Inhibitor Complex.

The heptose-less mutant of Escherichia coli, D31m4, bound complement subcomponent C1q and its collagen-like fragments (C1qCLF) with Ka values of 1.4 x 10(8) and 2.0 x 10(8) M-1 respectively. This binding was suppressed by chemical modification of C1q and C1qCLF using diethyl pyrocarbonate (DEPC). To investigate the role of lipopolysaccharides (LPS) in this binding, biosynthetically labelled [14C]LPS were purified from E. coli D31m4 and incorporated into liposomes prepared from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) [PC/PE/LPS, 2:2:1, by wt.]. Binding of C1q or its collagen-like fragments to the liposomes was estimated via a flotation test. These liposomes bound C1q and C1qCLF with Ka values of 8.0 x 10(7) and 2.0 x 10(7) M-1; this binding was totally inhibited after chemical modification of C1q and C1qCLF by DEPC. Liposomes containing LPS purified from the wild-strain E. coli K-12 S also bound C1q and C1qCLF, whereas direct binding of C1q or C1qCLF to the bacteria was negligible. Diamines at concentrations which dissociate C1 into C1q and (C1r, C1s)2, strongly inhibited the interaction of C1q or C1qCLF with LPS. Removal of 3-deoxy-D-manno-octulosonic acid (2-keto-3-deoxyoctonic acid; KDO) from E. coli D31m4 LPS decreases the binding of C1qCLF to the bacteria by 65%. When this purified and modified LPS was incorporated into liposomes, the C1qCLF binding was completely abolished. These results show: (i) the essential role of the collagen-like moiety and probably its histidine residues in the interaction between C1q and the mutant D31m4; (ii) the contribution of LPS, particularly the anionic charges of KDO, to this interaction.

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The function of pseudouridylic acid in transfer ribonucleic acid. Photochemical and chemical modification of formylmethionine tRNA of E. Coli

FEBS Letters ◽

10.1016/0014-5793(71)80033-9 ◽

1971 ◽

Vol 15 (2) ◽

pp. 105-110 ◽

Cited By ~ 12

Author(s):

M.A.Q. Siddiqui ◽

James Ofengand

Keyword(s):

Chemical Modification ◽

Ribonucleic Acid ◽

E Coli

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E. coli RNA polymerase promoters on superhelical SV40 DNA are highly selective targets for chemical modification

Nature ◽

10.1038/284640a0 ◽

1980 ◽

Vol 284 (5757) ◽

pp. 640-644 ◽

Cited By ~ 14

Author(s):

Patricia Hale ◽

Richard S. Woodward ◽

Jacob Lebowitz

Keyword(s):

Chemical Modification ◽

Rna Polymerase ◽

E Coli ◽

Sv40 Dna

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Studies on chemical modification of thionucleosides in the transfer ribonucleic acid of Escherichia coli

Biochemical Journal ◽

10.1042/bj1430285 ◽

1974 ◽

Vol 143 (2) ◽

pp. 285-294 ◽

Cited By ~ 11

Author(s):

Yarlagadda S. Prasada Rao ◽

Joseph D. Cherayil

Keyword(s):

Escherichia Coli ◽

Amino Acids ◽

Chemical Modification ◽

Gel Filtration ◽

Trna Synthetase ◽

Aminoacyl Trna Synthetase ◽

E Coli ◽

Chemical Reagents ◽

Mild Conditions ◽

Trna Species

35S-labelled tRNA from Escherichia coli was treated with chemical reagents such as CNBr, H2O2, NH2OH, I2, HNO2, KMnO4 and NaIO4, under mild conditions where the four major bases were not affected. Gel filtration of the treated tRNA showed desulphurization to various extents, depending on the nature of the reagent. The treated samples after conversion into nucleosides were chromatographed on a phosphocellulose column. NH2OH, I2 and NaIO4 reacted with all the four thionucleosides of E. coli tRNA, 4-thiouridine (s4U), 5-methylaminomethyl-2-thiouridine (mnm5s2U), 2-thiocytidine (s2C) and 2-methylthio-N6-isopentenyladenosine (ms2i6A), to various extents. CNBr, HNO2 and NaHSO3 reacted with s4U, mnm5s2U and s2C, but not with ms2i6A. KMnO4 and H2O2 were also found to react extensively with thionucleosides in tRNA. Iodine oxidation of 35S-labelled tRNA showed that only 6% of the sulphur was involved in disulphide formation. Desulphurization of E. coli tRNA with CNBr resulted in marked loss of acceptor activities for glutamic acid, glutamine and lysine. Acceptor activities for alanine, arginine, glycine, isoleucine, methionine, phenylalanine, serine, tyrosine and valine were also affected, but to a lesser extent. Five other amino acids tested were almost unaffected. These results indicate the fate of thionucleosides in tRNA when subjected to various chemical reactions and the involvement of sulphur in aminoacyl-tRNA synthetase recognition of some tRNA species of E. coli.

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