RESUMEN
In Neurospora crassa, the mutagenic process termed repeat-induced point mutation (RIP) inactivates duplicated DNA sequences during the sexual cycle by the introduction of C:G to T:A transition mutations. In this work, we have used a collection of N. crassa strains exhibiting a wide range of cellular levels of S-adenosylmethionine (AdoMet), the universal donor of methyl groups, to explore whether frequencies of RIP are dependent on the cellular levels of this metabolite. Mutant strains met-7 and eth-1 carry mutations in genes of the AdoMet pathway and have low levels of AdoMet. Wild type strains with high levels of AdoMet were constructed by introducing a chimeric transgene of the AdoMet synthetase (AdoMet-S) gene fused to the constitutive promoter trpC from Aspergillus nidulans. Crosses of these strains against tester duplications of the pan-2 and am genes showed that frequencies of RIP, as well as the total number of C:G to T:A transition mutations found in randomly selected am(RIP) alleles, are inversely correlated to the cellular level of AdoMet. These results indicate that AdoMet modulates the biochemical pathway leading to RIP.
Asunto(s)
ADN de Hongos/metabolismo , Metionina Adenosiltransferasa/genética , Neurospora crassa/genética , Mutación Puntual , Secuencias Repetitivas de Ácidos Nucleicos/fisiología , S-Adenosilmetionina/metabolismo , Alelos , Aspergillus nidulans/genética , Aspergillus nidulans/crecimiento & desarrollo , Aspergillus nidulans/metabolismo , Cruzamientos Genéticos , Genes Fúngicos , Neurospora crassa/enzimología , Neurospora crassa/crecimiento & desarrollo , Proteínas Recombinantes de Fusión/genética , Recombinación Genética , TransgenesRESUMEN
Trypanosoma cruzi trans-sialidase consists of a C-terminal domain composed essentially of immunodominant amino acid repeat units (SAPA-repeats) and an amino region responsible for the enzymatic activity (catalytic domain). To investigate the possible function(s) of SAPA-repeats, recombinant trans-sialidases either containing or lacking the C-terminal region were tested in mice. The presence of SAPA-repeats in the intravenously injected protein has two consequences. First, they enhance the persistence of the trans-sialidase activity in blood. Second, SAPA-repeats promoted the production of antibodies directed to the catalytic domain that inhibit trans-sialidase activity. These results suggest that SAPA-repeats modulate the trans-sialidase activity in blood.