Binding of Xenopus transcription factor A to 5S RNA and to single stranded DNA

Footprint competition assays are utilized to study the binding of Xenopus transcription factor A to a variety of single-stranded nucleic acids. The addition of Xenopus oocyte, yeast, or wheat germ 5S RNA as footprint competitors reveals that factor A binds these 5S RNAs with similar affinity. In contrast, factor A does not bind to E.coli 5S RNA or wheat germ tRNA in this assay. Factor A binding to single stranded DNA is also examined using footprint competition. Factor A binds preferentially to non-specific single stranded (M13) DNA versus double stranded (pBR322) DNA. Factor A binds equally well to single stranded DNA fragments containing either the coding or non-coding strands of the 5S RNA gene. Using single stranded M13 DNA as a competitor, the factor A-5S RNA gene complex is found to dissociate with a half-life of 5-6 min.