title: Evidence for dispensable sequences inserted into a nucleotide fold.
abstract: Previous experimental results along with the structural modeling presented indicate that a nucleotide fold starts in the amino-terminal part of Escherichia coli isoleucyl-transfer RNA synthetase, a single chain polypeptide of 939 amino acids. Internal deletions were created in the region of the nucleotide fold. A set of deletions that collectively span 145 contiguous amino acids yielded active enzymes. Further extensions of the deletions yielded inactive or unstable proteins. The three-dimensional structure of an evidently homologous protein suggests that the active deletions lack portions of a segment that connects two parts of the nucleotide fold. Therefore, the results imply that removal of major sections of the polypeptide that connects these two parts of the fold does not result in major perturbation of the nucleotide binding site.
authors.forename: R M
authors.initials: RM
authors.lastname: Starzyk
authors.forename: T A
authors.initials: TA
authors.lastname: Webster
authors.forename: P
authors.initials: P
authors.lastname: Schimmel
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases; D001426:Bacterial Proteins; D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology; D006860:Hydrogen Bonding; D007533:Isoleucine-tRNA Ligase; D008718:Methionine-tRNA Ligase; D011487:Protein Conformation; D012343:RNA, Transfer / Q000378:metabolism*; D013329:Structure-Activity Relationship; D046249:Transfer RNA Aminoacylation
chemical_list: D001426:Bacterial Proteins; D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases; D008718:Methionine-tRNA Ligase; D007533:Isoleucine-tRNA Ligase