Multiple factors involved in the transcription of class III genes in Xenopus laevis.

Cell-free extracts from Xenopus laevis oocytes (ovarian tissue), unfertilized eggs, embryos, and cultured kidney cells direct accurate transcription of cloned 5 S RNA and tRNA genes. Fractionation of these extracts by conventional ion exchange chromatography shows that multiple components are essential for the transcription of each of these genes by RNA polymerase III. Two chromatographically distinct fractions from ovary, egg, embryo, and kidney cell extracts are necessary and sufficient, in the presence of purified RNA polymerase III, for the transcription of tRNA genes. Transcription of 5 S RNA genes requires components present in these same fractions as well as the previously described 5 S gene-specific factor (TFIIIA). The analogous chromatographic fractions from different tissue extracts are functionally interchangeable, consistent with the suggestions that the endogenous factors which are necessary and sufficient for purified gene transcription are general (and not tissue-specific) factors.