Transcription factor IIIA gene expression in Xenopus oocytes utilizes a transcription factor similar to the major...

Xenopus transcription factor IIIA (TFIIIA) gene expression is stringently regulated during development. The steady-state level of TFIIIA mRNA in a somatic cell is approximately 10(6) times less than in an immature oocyte. We have undertaken studies designed to identify differences in how the TFIIIA gene is transcribed in oocytes and somatic cells. In this regard, we have localized an upstream transcriptional control element in the TFIIIA promoter that stimulates transcription from the TFIIIA promoter approximately threefold in microinjected oocytes. The upstream element, in cis. does not stimulate transcription from the TFIIIA promoter in somatic cells. Thus, the element appears to be oocyte specific in the context of the TFIIIA promoter. However, both oocytes and somatic cells contain a protein (or a related protein) that binds the upstream element. We have termed this protein from oocytes the TFIIIA distal element factor. The sequence of the upstream element is similar to the sequence of the upstream element found in the adenovirus major late promoter that is a binding site for the major late transcription factor. By gel shift analysis, chemical footprinting, methylation intereference, and point mutation analysis, we demonstrate that the TFIIIA distal element factor and major late transcription factor have similar DNA-binding properties.