Multiple SSAP binding sites constitute the stage-specific enhancer of the sea urchin late H1beta gene.
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 SpH1beta 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 H1beta 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.
Edelmann
L
L
Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Childs
G
G
D000818:Animals; D001665:Binding Sites; D001755:Blastocyst; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D004742:Enhancer Elements, Genetic; D005775:Gastrula; D018507:Gene Expression Regulation, Developmental; D006657:Histones / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D012617:Sea Urchins / Q000196:embryology / Q000235:genetics*
D004268:DNA-Binding Proteins; D006657:Histones; D011994:Recombinant Proteins; C079872:SSAP protein, sea urchin