Compensatory effect of distal promoter sequences on the basal expression of a microinjected 70-kilodalton heat shock protein gene after the midblastula transition of Xenopus laevis embryogenesis.

The promoter sequences involved in the basal expression of a human 70-kilodalton heat shock protein (HSP70) gene during Xenopus embryogenesis were analyzed by microinjection of mutant promoters of a HSP70--chloramphenicol acetyltransferase fusion gene into fertilized eggs and following their expression during early development. While deletion of the HSP70 gene promoter to--100 base pairs (bp) did not affect basal transcription in postmidblastula stage embryos, linker-scanner mutations in the CCAAT and purine box elements blocked expression. However, extension of the 5' boundary to--188 bp restored full wild-type expression to these mutants. These results suggest that multiple redundant cis-acting regulatory elements present in the human HSP70 gene promoter can function during Xenopus embryogenesis.