Nucleic acids binding properties of the C2-L1Tc Nucleic Acid Chaperone encoded by L1Tc Retrotransposon
Résumé
It has been reported that the C2-L1Tc protein located in the T. cruzi LINE L1Tc 3´ terminal end has nucleic acid chaperone (NAC) activity, an essential activity for retrotransposition of LINE-1. The C2-L1Tc protein contains two cysteine motifs of a C2H2 type, similar to those present in the transcription factor TFIIIA. The cysteine motifs are flanked by positively charged amino acid regions. The data presented in this paper shows that the C2-L1Tc recombinant protein has at least 16-fold higher affinity for single stranded than for double stranded nucleic acids and that it exhibits a clear preference for RNA binding over DNA. The C2-L1Tc binding profile (to RNA and DNA) corresponds to a non-cooperative binding model. The zinc fingers present in C2-L1Tc have different binding affinity to nucleic acid molecules and also different NAC activity. The RRR and RRRKEK (NLS) sequences as well as the C2H2 zinc finger located immediately downstream of these basic stretches are the main motifs responsible for the strong affinity of C2-L1Tc to RNA. These domains also contribute to bind single and double stranded DNA and have a duplex-stabilizing effect. However, the peptide containing the zinc finger situated towards the carboxyl terminal end of C2-L1Tc protein has a slight destabilization effect on a mismatched DNA duplex and shows a strong preference for single stranded nucleic acids, like C2-L1Tc. These results provide further insights into the essential properties of the C2-L1Tc protein as a nucleic acid chaperone.
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