Interaction of mtTFB and mtRNA polymerase at core promoters for transcription of Xenopus laevis mtDNA.

Transcription of Xenopus laevis mitochondrial DNA requires mtRNA polymerase and a dissociable factor, xl-mtTFB, that is distinct from the HMG-box factor known as mtTFA. This paper presents the purification of mtTFB and characterizes its DNA binding properties. xl-mtTFB activity copurifies with a 40-kDa polypeptide on silver-stained protein gels. Activity can be recovered following elution of this 40-kDa polypeptide from an SDS-polyacrylamide gel. xl-mtTFB is capable of binding to DNA, but this binding is relatively nonspecific and is easily competed by heterologous DNA.