title: Suppression of the acuH13 and acuH31 nonsense mutations in the carnitine/acylcarnitine translocase (acuH) gene of Aspergillus nidulans by the G265S substitution in the domain 2 of the release factor eRF1.
abstract: A search for suppressors of the carnitine/acylcarnitine translocase (CACT) deficiency in Aspergillus nidulans permitted the identification of the suaE7 mutation, mapping at a new translational suppressor (suaE) gene. The suaE gene is essential in A. nidulans and encodes the eukaryotic release factor 1 (eRF1). The suaE7 mutation suppresses two acuH alleles (acuH13 and acuH31), both carrying nonsense mutations in the CACT encoding gene that involve the replacement of a CAG (Gln) codon with a premature TAG stop codon. In contrast, the suaE7 gene does not suppress the acuH20 amber nonsense mutation involving a TGG-->TAG change. The phenotype associated to the suaE7 mutation strictly resembles that of mutants at the suaA and suaC genes, two translational suppressor genes previously identified, suggesting that their gene products might functionally interact in translation termination. Sequencing of the suaE7 gene allowed the identification of a mutation in the domain 2 of the omnipotent class-1 eukaryotic release factor involving the Gly265Ser substitution in the A. nidulans eRF1. This mutation creates a structural context unfavourable for normal eRF binding that allows the misreading of stop codons by natural suppressor tRNAs, such as the tRNAs(Gln). Structural analysis using molecular modelling of A. nidulans eRF1 domain 2 bearing the G265S substitution and computer simulation results suggest that this mutation might impair the necessary conformational changes in the eRF1 to optimally recognize the stop codon and simultaneously interact with the peptidyl transferase centre of the 60S ribosomal subunit.
authors.affiliation: Departamento de Microbiología y Parasitología, Facultad de Farmacia, Campus Universitario, Universidad de Alcalá, Carretera Madrid-Barcelona Km 33, Alcalá de Henares ES-28871, Madrid, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Martínez
authors.forename: Esther
authors.initials: E
authors.lastname: Marco
authors.forename: Federico
authors.initials: F
authors.lastname: Gago
authors.forename: Fernando
authors.initials: F
authors.lastname: Laborda
authors.forename: J
authors.initials: J
authors.lastname: Ramón De Lucas
mesh_terms: D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D002333:Carnitine Acyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018389:Codon, Nonsense; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010454:Peptide Termination Factors / Q000235:genetics*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D018389:Codon, Nonsense; D010454:Peptide Termination Factors; D002333:Carnitine Acyltransferases