Asunto(s)
Rol del Médico , Relaciones Médico-Paciente , Religión y Medicina , Religión , Conflicto de Intereses , Humanos , India , Estados UnidosRESUMEN
The complete amino acid sequence of elongation factor Tu of Escherichia coli has been established by sequencing overlapping cyanogen bromide and tryptic peptides. Sequence analysis of peptides was done primarily by solid-phase Edman degradation. Elongation factor Tu is a single chain polypeptide composed of 393 amino acids (Mr = 43,225). Its NH2 terminus is blocked with an acetyl group, as determined by mass spectroscopy, and lysine 56 is partially methylated. The cysteine residues associated with aminoacyl tRNA and guanosine nucleotide binding are located at positions 81 and 137, respectively. Although elongation factor Tu is coded for by two genes, the only site of microheterogeneity found was at the carboxyl terminus (residue 393), which is either glycine or serine. Comparison of the first 140 amino acids of elongation factor Tu and of elongation factor G shows a strong (31%) sequence homology. In addition, secondary structure calculations predict remarkable conformational similarities between the two proteins. The NH2-terminal region of elongation factor Tu appears to be composed of two beta-sheet domains connected by an exposed, alpha-helical bridge, which includes a 14-amino acid segment released by limited treatment with trypsin. Structural features of the aminoacyl-tRNA binding site are discussed in the light of sequence and other chemical and biochemical data.
Asunto(s)
Proteínas Bacterianas , Escherichia coli/metabolismo , Factores de Elongación de Péptidos , Secuencia de Aminoácidos , Proteínas Bacterianas/metabolismo , Bromuro de Cianógeno , Factor Tu de Elongación Peptídica , Factores de Elongación de Péptidos/metabolismo , Fragmentos de Péptidos/análisis , Conformación Proteica , Aminoacil-ARN de Transferencia/metabolismo , Ribosomas/metabolismo , TripsinaRESUMEN
A previously isolated mutant of E. coli K12 HAK 88 [Kuwano, M., Endo, h & yamamoto, M. (1972) J. Bacteriol, 112, 1150-1156], contains a new protein that in two-dimensional gel electropherorgrams has the same molecular weight as normal elongation factor Tu, but whose isoelectric point is altered approximately 0.1 pH unit in the acidic direction. Peptide mapping, purification properties and the ratio of leucyl plus isoleucyl to methionyl plus cysteinyl residues of the normal elongation factor Tu protein and the new protein show a close similarity between the two. The mutation causing the altered electrophoretic mobility is located between argH and rif (79 min on the E. coli genetic map). These biochemical and genetic data indicate that strain HAK 88 has a mutationally altered tufB gene.
Asunto(s)
Genes , Mutación , Factores de Elongación de Péptidos , Mapeo Cromosómico , Escherichia coli , Punto Isoeléctrico , Factores de Elongación de Péptidos/análisisRESUMEN
The amino acid sequence of elongation factor Tu (EF-Tu) from Escherichia coli has been determined. EF-Tu is a single-chain polypeptide composed of 393 amino acids (Mr 43,225 for the species bearing COOH-terminal serine). The NH2-terminal serine is acetylated, and lysine-56 is partially methylated. The sites of facile tryptic cleavage are at arginines 44 and 58 and at lysine-263. The cysteinyl residues associated with aminoacyl-tRNA and guanosine nucleotide binding activities are residues 81 and 137, respectively. The COOH-terminal amino acid is heterogenous in that analyses of the COOH-terminal peptides isolated from different EF-Tu preparations gave position 393 as glycine and serine in ratios (Gly/Ser) ranging from about 0.7 to 3.