Transcriptional control of spatially regulated genes in the early sea urchin embryo

by Zeller, Robert Werner

Abstract (Summary)
The regulatory domains of several Strongylocentrotus purpuratus embryo genes appear to be organized into "modules" of closely associated target sites for DNA-binding proteins. The Sp(G/C)F1 protein is a novel DNA-binding protein which binds specifically to G/C rich cis-elements. The protein was purified from embryo nuclear extracts by DNA affinity chromatography and the corresponding cDNA isolated. Five different Sp(G/C)F1 polypeptides, produced from a nested set of AUG initiation codons, are synthesized from a single mRNA template. Each protein shares a common C-terminus and a centrally located DNA-binding domain but incorporates variable amounts of an N-terminal proline-rich region. Since proline-rich regions often serve as transcriptional activation domains, the five Sp(G/C)F1 proteins are likely to possess different transcriptional "activation potentials." Sp(G/C)F1 proteins bind DNA cooperatively, most likely as homodimers, and multiple protein-DNA complexes are formed at high protein to DNA ratios in vitro. When bound to two or more target sites in the CyIIIa regulatory domain, the Sp(G/C)F1 polypeptides fouu protein-protein contacts, and "loop out" intervening regions of DNA which could allow the interaction of distant regulatory modules. The Sp(G/C)F1 protein is thus likely to serve as an intermodule communicator in the regulatory domains of many sea urchin embryo genes. Antibodies were used to quantitate the nuclear concentrations of two different DNA-binding proteins, P3A1 and P3A2, which bind specifically to P3A cis-elements found in several different regulatory domains. Both proteins are present maternally, but by late gastrula, P3A1 protein has disappeared from the nucleus leaving P3A2 protein levels relatively unchanged at about 10[superscript 4] molecules per nucleus. Since the relative binding affinities of P3A1 protein for different DNA target sites are up to 50X lower than the affinities of P3A2 protein for the same sites, P3A1 protein is therefore likely to be of functional significance only in early to mid-cleavage before genes known to contain P3A target sites, such as CyIIIa, SM50 and Specla, are expressed. The P3A1 and P3A2 proteins can thus serve as an antagonistic regulatory switch at P3A sites in cleavage stage sea urchin embryos.
Bibliographical Information:

Advisor:Scott E. Fraser; Leroy E. Hood; Howard D. Lipshitz; Paul W. Sternberg

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis



Date of Publication:11/30/1994

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