A Xenopus laevis gene encoding EF‐1αS, the somatic form of elongation factor 1α: Sequence, structure, and identification of regulatory elements required for embryonic transcription

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Abstract
Transcription of the Xenopus laevis EF-1αS gene commences at the mid-blastula stage of embryonic development and then continues constitutively in all somatic tissues. The EF-1αS promoter is extremely active in the early Xenopus embryo where EF-1αS transcripts account for as much as 40% of all new polyadenylated transcripts. We have isolated the Xenopus EF-1αS gene and used microinjection techniques to identify promoter elements responsible for embryonic transcription. These in vivo expression studies have identified an enhancer fragment, located approximately 4.4 kb upstream of the transcription start site, that is required for maximum expression from the EF-1αS promoter. The enhancer fragment contains both an octamer and a G/C box sequence, but mutation studies indicate that the octamer plays no significant role in regulation of EF-1αS expression in the embryo. The presence of a G/C element in the enhancer and of multiple G/C boxes in the proximal promoter region suggests that the G/C box binding protein, Spl, plays a major role in the developmental regulation of EF-1αS promoter activity.