Multiple SSAP binding sites constitute the stage-specific enhancer of the sea urchin late H1β gene

Lisa Edelmann, Geoffrey Childs

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The sea urchin late histone H1 genes are expressed at low levels up until mid-blastula stage of development when an enhancer element activates transcription to higher levels. Stage-specific activator protein (SSAP) was previously identified as the transcription factor that binds to a sequence motif within the late H1-specific enhancer, USE IV, and mediates this stage- specific activation. However, another conserved late H1-specific element, USE III, was also shown to contribute to the activated expression of the late H1 genes. To attain a better understanding of the mechanism of blastula stage activation an extended analysis of the late H1-specific DNA sequences of the SpH1β gene was performed. Our findings indicate that this region, located between positions -320 and -200, consists of three SSAP binding sites, USE IV, USE III, and another site located between the two, termed Site 2. Although SSAP binds to USE IV in vitro with 10-15-fold higher affinity than to either of the other two sites, multiple sites are necessary for activation. Multimers of either USE IV or USE III activate mid-blastula stage transcription to similar levels in the context of a functional H1β basal promoter, but not with a TATA box alone. In addition, multimers of USE IV activate expression of a reporter construct containing an early histone H1 promoter at an embryonic stage when it is normally repressed. We propose a mechanism for mid-blastula activation of the late histone H1 genes where SSAP binding sites activate expression, but require the presence of the cis sequences of the basal promoter to function.

Original languageEnglish (US)
Pages (from-to)133-147
Number of pages15
JournalGene expression
Issue number3
StatePublished - 1998


  • Histone genes
  • SSAP binding sites
  • Sea urchin

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics


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