Selective modification of cytidine, uridine, guanosine and pseudouridine residues in Escherichia coli leucine transfer ribonucleic acid |
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Authors: | S E Chang D Ish-Horowicz |
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Affiliation: | Medical Research Council, Laboratory of Molecular Biology Hills Road, Cambridge, CB2 2QH, England |
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Abstract: | The specificity of methoxyamine for the cytidine residues in an Escherichia coli leuoine transfer RNA (tRNA1leu is described in detail. Of the six non-hydrogen-bonded cytidine residues in the clover-leaf model of this tRNA, four are very reactive (C-35, 53, 85 and 86) and two are unreactive (C-67 and 79).The specificity of l-cyclohexyl-3-[2-morpholino-(4)-ethyl]carbodiimide methotosylate for the uridine, guanosine and pseudouridine residues in the leucine tRNA was also investigated. The carbodiimide completely modified four uridine residues (U-33, 34, 50 and 51) and partially modified G-37 and Ψ-39. For technical reasons, the sites of partial modification in loop I of the tRNA were difficult to establish. There was no modification of base residues in loop IV nor of U-59 at the base of stem e of the tRNA.The modification patterns described for the leucine tRNA are compared with those observed for the E. coli initiator tRNA1met and su+III tyrosine tRNA. Several general conclusions regarding tRNA conformation are made. In particular, the evidence supporting a diversity of anticodon loop structures amongst tRNAs is discussed. |
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