Point mutational analysis of the Xenopus laevis 5S gene promoter.

We have introduced C to T transitions into GC and CG base pairs of the Xenopus laevis somatic 5S gene coding region and its 5' flank in order to analyse their effects on transcription activity and regulation. These studies allow us to differentiate between the two promoter elements and their spacer, within the internal control region. Mutations within the 5' element which dissent from the corresponding tRNA consensus sequence reduce transcription activity substantially without significantly affecting transcription factor (TF) III A binding. Mutations in the spacer region have no pronounced effect on transcription. The 3' promoter element is found to extend to position 97, since mutations in this region interfere with transcription activity. This may be, at least partially, attributable to a reduced competition strength for TF III A.