An enhancer responsible for activating transcription at the midblastula transition in Xenopus development.

Transcripts from the Xenopus gene GS17 are absent from oocytes and first appear at the midblastula transition (MBT), about 8 hr after fertilization. Injection experiments with deletions of the GS17 gene and GS17-beta-globin hybrid genes show that a relatively short sequence of 74 base pairs is sufficient to activate, in cis, transcription at the MBT. This 74-base sequence is located about 700 bases upstream of the GS17 promoter and has the properties of an enhancer element.