title: RNA minihelices as model substrates for ATP/CTP:tRNA nucleotidyltransferase.
abstract: Twenty-one RNA minihelices, resembling the coaxially stacked acceptor- /T-stems and T-loop found along the top of a tRNA's three-dimensional structure, were synthesized and used as substrates for ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli and Saccharomyces cerevisiae. The sequence of nucleotides in the loop varied at positions corresponding to residues 56, 57 and 58 in the T-loop of a tRNA. All minihelices were substrates for both enzymes, and the identity of bases in the loop affected the interaction. In general, RNAs with purines in the loop were better substrates than those with pyrimidines, although no single base identity absolutely determined the effectiveness of the RNA as substrate. RNAs lacking bases near the 5'-end were good substrates for the E. coli enzyme, but were poor substrates for that from yeast. The apparent Km values for selected minihelices were 2-3 times that for natural tRNA, and values for apparent Vmax were lowered 5-10-fold.
authors.affiliation: Department of Chemistry, Clark University, 950 Main Street, Worcester, MA 01610, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Sun
authors.forename: D L
authors.initials: DL
authors.lastname: Thurlow
mesh_terms: D001345:Autoradiography; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012313:RNA / Q000737:chemistry / Q000378:metabolism*; D012316:RNA Nucleotidyltransferases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013329:Structure-Activity Relationship
chemical_list: D012313:RNA; D012316:RNA Nucleotidyltransferases; C023198:tRNA nucleotidyltransferase