Leu Codon Research Articles

Beta 141 Leu is not deleted in the unstable haemoglobin Atlanta-Coventry but is replaced by a novel amino acid of mass 129 daltons.

Reinvestigation of the structure of the beta-chain of Hb Atlanta-Coventry (beta 75 Leu----Pro, beta 141 Leu deleted) confirmed the presence of two abnormalities; however, analysis of the aberrant beta Co14 tryptic peptide by liquid secondary ion mass spectrometry indicated that the beta 141 Leu (mass 113 daltons) was not deleted but replaced by a novel amino acid of mass 129 daltons. The new amino acid in peptide beta Co14 was uncharged at pH 6.5, more hydrophillic than leucine and susceptible to cleavage by both chymotrypsin and carboxypeptidase A. We propose that the new residue is likely to be hydroxyleucine and that it results from post-translational oxidation of beta 141 Leu as a consequence of perturbation of the haem environment caused by the beta 75 Leu----Pro mutation in the E helix (E19). This proposal is entirely consistent with recent DNA analysis which showed that beta At-Co was not the product of a third beta-globin gene and that neither of the two beta-globin genes, beta A nor beta Atlanta, contained a deletion of the beta 141 Leu codon. We have subsequently found this modified amino acid at position beta 141 in two other unstable haemoglobins, both of which involve mutations on the haem side of the E helix.

A single base change in the acceptor stem of tRNA(3Leu) confers resistance upon Escherichia coli to the calmodulin inhibitor, 48/80.

We have isolated several classes of spontaneous mutants resistant to the calmodulin inhibitor 48/80 which inhibits cell division in Escherichia coli K12. Several mutants were also temperature sensitive for growth and this property was exploited to clone a DNA fragment from an E. coli gene library restoring growth at 42 degrees C and drug sensitivity at 30 degrees C in one such mutant. Physical and genetic mapping confirmed that both the mutation and the cloned DNA were located at 15.5 min on the E. coli chromosome at a locus designated feeB. By subcloning, complementation analysis and sequencing, the feeB locus was identified as identical to the tRNA(CUALEU) gene. When the mutant locus was isolated and sequenced, the mutation was confirmed as a single base change, C to A, at position 77 in the acceptor stem of this rare Leu tRNA. In other studies we obtained evidence that this mutant tRNA, recognizing the rare Leu codon, CUA, was defective in translation at both permissive and non-permissive temperatures. The feeB1 mutant is defective in division and shows a reduced growth rate at non-permissive temperature. We discuss the possibility that the mutant tRNA(3Leu) is limiting for the synthesis of a polypeptide(s), requiring several CUA codons for translation which in turn regulates in some way the level or activity of the drug target, a putative cell cycle protein.

The delta beta crossover region in Lepore boston hemoglobinopathy is restricted to a 59 base pairs region around the 5' splice junction of the large globin gene intervening sequence

Genomic DNA from a hemoglobin (Hb) Lepore Boston (delta 87 Gln beta 116 His) homozygote of Southern Italian origin has been studied in order to map the fusion point between the delta and beta genes. An Ava II restriction endonuclease recognition sequence, located 12 base pairs (bp) downstream from the 5' end of the beta gene large intervening sequence, has been taken as marker of the beta-like portion of the fusion gene. This site was present even in the delta beta gene, allowing the localization of the crossover area to a 59-bp region extending from the first nucleotide of the Leu codon in position 88 to the 11th nucleotide of the large intervening sequence. The analysis of the DNA restriction polymorphisms in the gamma delta beta globin gene region provides evidence that a single mutational event originated the Lepore delta beta genes, at least in the Italian population.