Sequences preceding the minimal promoter of the Xenopus somatic 5S RNA gene increase binding efficiency for transcription factors.

Sequences preceding the minimal promoter play a role in the differential expression of the Xenopus somatic and oocyte-type 5S RNA genes. In this report, the somatic sequences between -32 and +37 are shown to increase transcriptional activity in microinjected embryos, yet have little to no effect in microinjected oocyte nuclei. In vitro, these sequences increase activity in whole oocyte S150 extracts, but not in oocyte nuclear extracts. In S150 extracts, these somatic sequences facilitate binding by a commonly required factor(s), other than TFIIIA, which forms a stable complex with the 5S gene. This transcriptional enhancement is also apparent in a reconstituted system using purified TFIIIA and partially purified TFIIIB and TFIIIC.