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  • FPG had no consistent activity in reducing G T

    2022-05-13

    FPG-2 had no consistent activity in reducing G→T transversions. Gao and Murphy [2] earlier reported that FPG-2 had a limited amount of activity in vitro on depurinated, UV-treated, and methylene-blue-treated DNA (but not on 8-oxo-G-containing oligonucleotides). FPG-2 contains the N-terminal domain and the H2TH motif in the C-terminal domain, but lacks the FPG-1 C-terminal sequence that corresponds to the bacterial zinc-finger motif [13]; this motif contributes to stabilization of the enzyme–DNA complex [14]. Other products of the Arabidopsisfpg gene splicing variants found from cloning and RT-PCR screens were not tested, but most of these are predicted to lack essential active site amino acids or have other major disruptions in their C-terminal amino SB742457 sequences [1], so it seems unlikely that they would be active. The present experiments were performed in order to determine whether evolution of the ArabidopsisFpg or Ogg genes produced enzymes with specificities other than, or in addition to, the removal of 8-oxo-G. In unirradiated cells we found a strong effect of FPG-1 in reducing GC→AT transitions in HS1192 and AT→TA transversions in HS1195 and of OGG in reducing AT→TA transversions in HS1195 (Table 2). In irradiated cells, the results were similar, except that the effect of OGG on GC→AT transitions in HS1192 became evident. FPG from E. coli is known to recognize and remove Fapy-A and other altered bases in vitro [15], but Palmer et al. [6] did not find substantial differences in the reversion rates of far-UV-irradiated HS1192 or HS1195 strains possessing or lacking the E. colifpg gene. Thus these results imply that Arabidopsis FPG-1 and OGG recognize and remove a more extensive set of altered bases than does E. coli FPG. However, it is not yet clear what these altered bases are or whether the processes leading to reversion to lacZ+ are as direct for HS1192 and HS1195 as are those for HS1194 (Fig. 4). Surprisingly, FPG-1 appeared to increase the frequency of reversion of the lacZ gene in HS1191 (Table 2, Table 3). Some of these reversions were apparently due to second-site mutations, because base-sequence analysis indicated no difference at position 461. In natural systems, the enzymes of base-excision repair act in complexes (e.g., [16]); it may be that the presence of the plant FPG-1 affects the operation of the repair DNA polymerase. We note that if FPG-1 stimulated AT→CG transversion, it would have the effect of both limiting HS1194 reversion and promoting HS1191 reversion. Because only plants among eukaryotes have the fpg gene, it is probable that they obtained the gene in the evolutionary events that led to the incorporation of plastids into primordial plant cells. This raises the question of how the various glycosylases are targeted to the locations of the three genomes, nucleus, mitochondrion, and plastid, in the plant cell. The mammalian ogg gene produces several initiation and splicing variants of mRNA [17], some products of which are targeted to the mitochondria and some to the nucleus. In contrast, the Arabidopsisogg gene produces only one type of mRNA by splicing [8]. To our knowledge, there is as yet no evidence for the targeting of plant OGG or FPG proteins to various organelles, but Arabidopsis OGG is predicted through sequence analysis to be localized in mitochondria or plastids [18] and Arabidopsis FPG-1 has a predicted nuclear localization signal [12]. These predictions are opposite to what might be expected from evolutionary considerations. Direct measurements are essential to clarify this point.
    Acknowledgment
    Introduction Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, a condition that currently affects around 5.7 million people in Latin America, causing negative social effects and healthcare burden (Bern, 2015, Organization, W. W. H, 2015, Rassi et al., 2010). This parasite belongs to Kinetoplastida, a class that comprises unicellular flagellated protists, characterized by the presence of the kinetoplast, a DNA-containing granule localized inside their single mitochondrion (Rodrigues et al., 2014).