Abstract
Nucleic acid chaperone activity is an essential component of reverse transcription in retroviruses and retrotransposons. Using DNA stretching with optical tweezers, we have developed a method for detailed characterization of nucleic acid chaperone proteins, which facilitate the rearrangement of nucleic acid secondary structure. The nucleic acid chaperone properties of the human immunodeficiency virus type-1 (HIV-1) nucleocapsid protein (NC) have been extensively studied, and duplex destabilization, nucleic acid aggregation, and rapid protein binding kinetics have been identified as major components of its activity. The chaperone properties of other nucleic acid chaperone proteins, such as those from the retrotransposons LINE-1 and Ty3, ORF1p and Ty3 NC, are not well understood. We used single molecule DNA stretching to characterize the activity of wild type and mutant ORF1p and Ty3 NC. ORF1p binds both double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) with high affinity, and strongly aggregates both forms. It is therefore an excellent chaperone, and altering certain residues has dramatic effects on chaperone activity. Wild type Ty3 also strongly aggregates both dsDNA and ssDNA, and melted DNA exhibits more rapid reannealing in the presence of Ty3 NC, relative to that observed in the presence of ORF1p. We examine several Ty3 NC mutants to identify the roles of functional regions of the protein in its chaperone activity. This research was supported in part by funding from INSERM and ANRS (France).
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