Positive and negative regulation of the gene for transcription factor IIIA in Xenopus laevis oocytes.

Expression of the positively acting 5S gene-specific transcription factor, TFIIIA, is regulated during development, with highest levels of mRNA and protein occurring during oogenesis. By analysis of TFIIIA promoter mutants microinjected into late stage Xenopus oocytes, we have determined DNA sequences required for the transcription of this gene and we have identified proteins that bind to these regulatory sequences. A negative element lies between positions -306 and -289. Three positive-acting sequences are located between positions -289 and -253, -250 and -173, and -144 and -101. Gel shift analyses of TFIIIA promoter fragments incubated with Xenopus oocyte extracts have identified two DNA-protein complexes. One complex, designated B1, requires sequences within the promoter region extending from -271 to -253 while the second complex, designated B2, involves promoter sequences from -235 to -221. The protein involved in formation of the B1 complex has been found to be related to the human adenovirus major late transcription factor, USF.