Embryonic transcriptional activation of aXenopus cytoskeletal actin gene does not require a serum response element

The Serum Response Element (SRE) is a sequence motif which activates transcription of certain genes in response to factors that stimulate cell proliferation. This motif is found in the promoter of aXenopus laevis cytoskeletal actin gene, which is transcriptionally activated very early in embryonic development. We tested whether the SRE plays a role in the developmentally-timed transcriptional activation of this gene by constructing an SRE replacement mutant and studying its transcription after microinjection intoXenopus embryos. Normal amounts of actin mRNA are transcribed at the normal time in development from this mutant, suggesting that the SRE is not the sole determinant of temporal specificity of actin gene transcription in the embryo.