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Mem. Inst. Oswaldo Cruz ; 102(6): 757-762, Sept. 2007. ilus, graf, tab
Article in English | LILACS | ID: lil-463485


The kinetoplast genetic code deviates from the universal code in that 90 percent of mitochondrial tryptophans are specified by UGA instead of UGG codons. A single nucleus-encoded tRNA Trp(CCA) is used by both nuclear and mitochondria genes, since all kinetoplast tRNAs are imported into the mitochondria from the cytoplasm. To allow decoding of the mitochondrial UGA codons as tryptophan, the tRNA Trp(CCA) anticodon is changed to UCA by an editing event. Two tryptophanyl tRNA synthetases (TrpRSs) have been identified in Trypanosoma brucei: TbTrpRS1 and TbTrpRS2 which localize to the cytoplasm and mitochondria respectively. We used inducible RNA interference (RNAi) to assess the role of TbTrpRSs. Our data validates previous observations of TrpRS as potential drug design targets and investigates the RNAi effect on the mitochondria of the parasite.

Animals , RNA Interference , RNA, Protozoan/metabolism , RNA, Transfer/metabolism , Trypanosoma brucei brucei/enzymology , Tryptophan-tRNA Ligase/metabolism , Gene Expression , RNA, Protozoan/genetics , RNA, Transfer/genetics , Time Factors , Trypanosoma brucei brucei/cytology , Trypanosoma brucei brucei/genetics , Tryptophan-tRNA Ligase/genetics
J Biosci ; 2006 Jun; 31(2): 281-9
Article in English | IMSEAR | ID: sea-110948


Ribosome recycling is a process which dissociates the post-termination complexes (post-TC) consisting of mRNA-bound ribosomes harbouring deacylated tRNA(s). Ribosome recycling factor (RRF), and elongation factor G (EFG) participate in this crucial process to free the ribosomal subunits for a new round of translation. We discuss the over-all pathway of ribosome recycling in eubacteria with especial reference to the important role of the initiation factor 3 (IF3) in this process. Depending on the step(s) at which IF3 function is implicated, three models have been proposed. In model 1, RRF and EFG dissociate the post-TCs into the 50S and 30S subunits, mRNA and tRNA(s). In this model, IF3, which binds to the 30S subunit, merely keeps the dissociated subunits apart by its anti-association activity. In model 2, RRF and EFG separate the 50S subunit from the post-TC. IF3 then dissociates the remaining complex of mRNA, tRNA and the 30S subunit, and keeps the ribosomal subunits apart from each other. However, in model 3, both the genetic and biochemical evidence support a more active role for IF3 even at the step of dissociation of the post-TC by RRF and EFG into the 50S and 30S subunits.

Models, Genetic , Peptide Chain Termination, Translational , Prokaryotic Initiation Factor-3/chemistry , Protein Subunits/metabolism , RNA, Messenger/metabolism , RNA, Transfer/metabolism , Ribosomes/metabolism
Indian J Biochem Biophys ; 1994 Dec; 31(6): 454-8
Article in English | IMSEAR | ID: sea-29087


Total tRNAs isolated from N2- and NH4(+)-grown Azospirillum lipoferum cells were compared with respect to amino acid acceptance, isoacceptor tRNA species levels and extent of nucleotide modifications. Amino-acylation of these two tRNA preparations with ten different amino acids indicated differences in the relative acceptor activities. Comparison of aminoacyl-tRNA patterns by RPC-5 column chromatography revealed no qualitative differences in the elution profiles. However, quantitative differences in the relative amounts of some isoacceptors were observed. These results indicate that alterations of relative amounts of functional tRNA species occur to match cellular requirements of the bacterial cells using N2 or NH4+ as nitrogen source. In addition, the content of modified nucleotides in total tRNAs of N2- and NH4(+)-grown cells was determined. In the NH4(+)-grown cells, content of most of the modified nucleotides decreased significantly. Based upon these results, the relationship of chargeability of tRNAs to base modifications is discussed.

Acylation , Amino Acids/metabolism , Azospirillum/drug effects , Nitrogen/pharmacology , Nucleotides/metabolism , Quaternary Ammonium Compounds/pharmacology , RNA Processing, Post-Transcriptional , RNA, Transfer/metabolism