Characterization of a Xenopus oocyte factor that binds to a developmentally regulated cis-element in the TFIIIA gene

TFIIIA mRNA expression is developmentally regulated during Xenopus oogenesis. We have identified a positive-acting cis-element in the TFIIIA gene located between -671 and -629 with respect to the mRNA initiation site, termed element 3. Element 3 contributes to the efficient transcription of the TFIIIA gene in stage III oocytes, but is inactive in the normal context of the TFIIIA gene in stage VI oocytes. A trans-acting factor, termed B3, in immature ovary extracts binds to a region within element 3 containing four repeats of the consensus nucleotide sequence 5' (T/A)GGTTACT. We discuss how the developmental regulation of B3-element 3 function could be achieved in the context of the TFIIIA gene during oogenesis.