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A conserved element in the protein-coding sequence is required for normal expression of replication-dependent histone
A Ficzycz1, N K Kaludov, Z Lele
1Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
Developmental Biology
|February 1, 1997
Summary
The CRAS alpha element (coding region activating sequence alpha) is crucial for replication-dependent histone gene expression in developing Xenopus embryos. Its mutation significantly reduces gene expression, highlighting its developmental role.
Area of Science:
- Developmental Biology
- Molecular Genetics
- Gene Regulation
Background:
- Replication-dependent histone genes in mammals and amphibians share a conserved regulatory element, the CRAS alpha element (coding region activating sequence alpha), within their coding sequences.
- The CRAS alpha element's role in histone gene expression during development, particularly in Xenopus, has not been previously investigated.
- Xenopus development involves a critical switch in histone gene expression from replication-independent in oocytes to replication-dependent after the midblastula transition.
Purpose of the Study:
- To investigate the function of the CRAS alpha element in regulating histone gene expression during Xenopus development.
- To determine if the CRAS alpha element mediates the switch to replication-dependent histone gene expression in Xenopus embryos.
Main Methods:
- In vivo expression experiments using wild-type and alpha-mutant mouse H3.2 genes in Xenopus.
- Analysis of alpha sequence-specific DNA-binding activities in oocyte and embryonic nuclear extracts using electrophoretic mobility shift assays.
- Estimation of molecular masses and assessment of phosphorylation effects on DNA-binding factors.
Main Results:
- Mutation of the CRAS alpha element led to a fourfold decrease in H3.2 gene expression in Xenopus embryos, but not in oocytes.
- Two distinct alpha sequence-binding activities were identified: a constant slow-migrating complex and a rapidly migrating complex whose levels varied during development.
- The rapidly migrating complex, attributed to an 85 kDa factor, showed increased DNA-binding activity in its dephosphorylated state, correlating with the onset of replication-dependent histone gene expression after the midblastula transition.
Conclusions:
- The CRAS alpha element is essential for normal replication-dependent histone gene expression in Xenopus embryos.
- The developmental regulation of the 85 kDa alpha-binding factor, influenced by phosphorylation, likely plays a key role in mediating replication-dependent histone gene expression.
- The conserved CRAS alpha element is a critical component for coordinating histone gene expression with the cell cycle during Xenopus development.