F. Palla et al., SEA-URCHIN EARLY HISTONE H2A MODULATOR BINDING FACTOR-I IS A POSITIVETRANSCRIPTION FACTOR ALSO FOR THE EARLY HISTONE H3 GENE, Proceedings of the National Academy of Sciences of the United Statesof America, 90(14), 1993, pp. 6854-6858
To shed some light on the mechanisms involved in the coordinate regula
tion of the early histone gene set during sea urchin development, we t
ested the hypothesis that the upstream sequence element USE1, previous
ly identified in the early H2A modulator, could also participate in th
e transcription of the early histone H3 gene. We found by DNase I prot
ection analysis and by competition in electrophoretic mobility-shift e
xperiments that two sequence elements of the H3 promoter closely resem
bled the USE1-H2A sequence in their binding activity for nuclear facto
rs from 64-cell stage embryos. These modulator binding factor 1 (MBF-1
)-related factors seem to recognize the ACAGA motif that is conserved
between the USE1-like sequences of both H2A and H3 promoters. In fact,
excess oligonucleotide containing a mutated USE1-H2A element in which
the ACAGA sequence was mutated to AGTCA failed to compete with the US
E1 sites of both H2A and H3 genes for interaction with MBF-1. Finally,
in vivo transcriptional analysis in both Xenopus and sea urchin showe
d that an excess of USE1-H2A element efficiently competed for the acti
vity of the H3 promoter. From these results we conclude that MBF-1 is
a transcription factor conserved between sea urchin and frog and that
MBF-1 or related transcription factors are involved in the coordinate
expression of both H2A and H3 early histone genes.