Xenopus transcription factor A promotes DNA reassociation.

We demonstrate by agarose gel electrophoresis and DNase I footprinting that Xenopus transcription factor A promotes DNA reassociation. This ability of factor A is dependent upon the domain-like structure of the protein. Digestion of factor A by papain results in a protein fragment which promotes DNA reassociation whereas a smaller fragment obtained by trypsin digestion does not. Although factor A requires zinc for specific binding to the 5 S RNA gene, the metal is not required for single-stranded DNA binding or promotion of DNA reassociation by this protein. The factor A-dependent renaturation of the 5 S RNA gene from its individual 32P end-labeled strands results in the proper gene conformation as evidenced by the restoration of the DNase I footprint characteristic of the intragenic control region. Alterations in DNase I cleavage patterns induced by factor A on the individual 5 S DNA strands are distinct from those induced by the protein on the duplex 5 S RNA gene. The ability of factor A to promote DNA reassociation further defines the possible roles of this protein in the formation of active transcription complexes and their maintenance during repeated rounds of transcription.