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Upstream sequences required for tissue‐specific activation of the cardiac actin gene in Xenopus laevis embryos.

The entire DNA sequence of the Xenopus laevis cardiac actin gene was determined. A recombinant plasmid comprising the cardiac actin gene promoter fused to the bacterial chloramphenicol acetyl transferase (CAT) gene is correctly regulated after introduction into fertilized Xenopus eggs. The fusion gene shows a temporal and tissue‐specific pattern of expression in the early embryo which is indistinguishable from that of the endogenous cardiac actin gene. The fusion gene is also activated in cultured embryo fragments that are induced by cell interactions to form embryonic muscle tissue. Tissue‐specific expression of the recombinant requires sequences between 217 and 416 nucleotides upstream from the transcription initiation site. In contrast, both the chimaeric gene and the entire cardiac actin gene are expressed at a basal level after microinjection into Xenopus oocytes, requiring only the presence of a TATA box upstream from the cap site.