The L1Tc C-Terminal Domain from Trypanosoma cruzi Non-Long Terminal Repeat Retrotransposon Codes for a Protein That Bears Two C₂H₂ Zinc Finger Motifs and Is Endowed with Nucleic Acid Chaperone Activity

Abstract

L1Tc, a non-long terminal repeat retrotransposon from Trypanosoma cruzi, is a 4.9-kb actively transcribed element which contains a single open reading frame coding for the machinery necessary for its autonomous retrotransposition. In this paper, we analyze the protein encoded by the L1Tc 3′ region, termed C2-L1Tc, which contains two zinc finger motifs similar to those present in the TFIIIA transcription factor family. C2-L1Tc binds nucleic acids with different affinities, such that RNA > tRNA > single-stranded DNA > double-stranded DNA, without any evidence for sequence specificity. C2-L1Tc also exhibits nucleic acid chaperone activity on different DNA templates that may participate in the mechanism of retrotransposition of the element. C2-L1Tc promotes annealing of complementary oligonucleotides, prevents melting of perfect DNA duplexes, and facilitates the strand exchange between DNAs to form the most stable duplex DNA in competitive displacement assays. Mapping of regions of C2-L1Tc using specific peptides showed that nucleic acid chaperone activity required a short basic sequence accompanied by a zinc finger motif or by another basic region such as RRR. Thus, a short basic polypeptide containing the two C₂H₂ motifs promotes formation of the most stable duplex DNA at a concentration only three times higher than that required for C2-L1Tc.

ACKNOWLEDGMENTS

We are grateful to M. E. Patarroyo, E. Torres, and F. Guzman for peptide synthesis and purification. We thank M. Caro and D. Branciforte for technical assistance and A. Berzal and his team for assistance in RNA transcription assays.

This work was supported by FIS 01/3148 and RICET C03-04 from Fondo de Investigación Sanitaria, MSC, and BMC2003-00834 from Plan Nacional I+D+I (MEC), Spain. S.R.H. was supported by an MEC predoctoral fellowship (FPU), J.L.G.-P. was supported by a Fundación Ramón Areces predoctoral fellowship, and S.L.M. was supported by NIH grant GM 40367.