Nucleic-acid-binding properties of the C2-L1Tc nucleic acid chaperone encoded by L1Tc retrotransposon

Abstract

It has been reported previously that the C2-L1Tc protein located in the Trypanosoma cruzi LINE (long interspersed nuclear element) L1Tc 3′ terminal end has NAC (nucleic acid chaperone) 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 TFIIIA (transcription factor IIIA). The cysteine motifs are flanked by positively charged amino acid regions. The results of the present study show that the C2-L1Tc recombinant protein has at least a 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-co-operative-binding model. The zinc fingers present in C2-L1Tc have a different binding affinity to nucleic acid molecules and also different NAC activity. The RRR and RRRKEK [NLS (nuclear localization sequence)] 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 C-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, such as C2-L1Tc. These results provide further insight into the essential properties of the C2-L1Tc protein as a NAC.

The Trypanosomatid Pr77-hallmark contains a downstream core promoter element essential for transcription activity of the Trypanosoma cruzi L1Tc retrotransposon

“…Pr77 promoter–derived unspliced transcripts initiate at or close to nucleotide +1 and are efficiently translated [ 11 ]. L1Tc has coding capacity for an apurinic/apyrimidinic (AP) endonuclease (with 3′ phosphatase and 3′ phosphodiesterase activities [ 12 – 14 ], a reverse transcriptase [ 15 ], RNaseH [ 16 ], and a nucleic acid chaperone [ 17 , 18 ]. It also codes for an in vitro- and in vivo -active, self-cleaving 2A sequence (L1Tc2A) that may well determine the composition and proportions of the products translated from L1Tc [ 19 ].…”

Identification of an hepatitis delta virus-like ribozyme at the mRNA 5′-end of the L1Tc retrotransposon from Trypanosoma cruzi

“…L1Tc is actively transcribed as a polyadenylated mRNA ( 7 ). It codes for the enzyme machinery involved in TPRT, including an apurinic/apyrimidinic (AP) endonuclease ( 7 , 8 ), 3′-phosphatase, 3′-phosphodiesterase, a reverse transcriptase ( 9 ), RNase H ( 10 ) and a nucleic acid chaperone ( 11 , 12 ). L1Tc also bears at its N-terminal end a functional 2A-autoproteolitic sequence ( 13 ) similar to that found in small-size RNA viruses.…”

Pr77 and L1TcRz

“…L1Tc is a LINE element that codes for the mobilization machinery including AP-endonuclease, 9 , 10 reverse transcriptase, 11 RNase H 12 and nucleic acids chaperone activities. 13 , 14 In addition, an active picornavirus-like 2A autoproteolytic motif resides at the N-terminal end of the encoded L1Tc polypeptide. The 2A autoproteolytic activity is expected to regulate the composition and abundance of the enzymatic machinery required for autonomous mobilization of L1Tc.…”