Structural Studies of regulators of histone protein synthesis
EMSL Project ID
16290
Abstract
The main objective of this proposal is to provide a structural basis for regulation of histone protein synthesis. For most eukaryotic mRNAs which are polyadenylated, the rate limiting step in translation initiation involves the binding of the 40S subunit of the ribosome to the mRNA, via specific interactions between the 40S ribosome associated protein eIF3 and the mRNA-associated protein eIF4G. eIF4G interacts with both the 5? cap structure via interactions with the cap-binding protein eIF4E, and with the 3? poly(A) tail via interactions with poly A binding protein (PABP), thereby bridging the 3? and 5? untranslated regions of the mRNA. The assembly of this macromolecular complex serves to circularize the mRNA. Histone genes are the only genes that are not polyadenylated, and the poly(A) tail is replaced by a stem-loop structure which binds the protein Stem-loop binding protein (SLBP). The SLBP/RNA complex is important for the recruitment and assembly of multi-protein-RNA complexes that regulate histone gene expression. Previous biological studies have demonstrated that similar to PABP, SLBP also stimulates the translation of histone mRNAs in vitro and in vivo, and this up-regulation occurs in a cap-dependent manner via a 13 amino acid motif that is conserved in SLBP from higher eukaryotes. More recently, Bill Marzluff?s laboratory (UNC-CH) has identified a protein called AD2 using the yeast 2-hybrid system with SLBP as a bait. This protein interacts specifically with the translation activation region of SLBP, and stimulates histone gene translation in Xenopus oocytes (see preliminary results). Our current model is that AD2 forms a bridge between SLBP and the initiation complex at the 5? end of the mRNA. In order to understand the molecular basis for the SLBP/AD2 interaction, we have initiated high resolution NMR studies on SLBP as well as AD2. NMR studies on SLBP show clearly that it is intrinsically disordered in solution, in the absence of its protein targets. Our preliminary NMR and biophysical characterization of AD2 suggests that the protein is helical, and is a symmetric homo-dimer with a net molecular weight of 54 kDa. The overall goal of this proposal is to determine the solution structure and dynamics of AD2 in the absence and presence of the N-terminal domain of SLBP so as to characterize the structural transitions important for the assembly of the translation initiation complex. Given the large size of AD2 we will rely of TROSY-based approaches for obtaining assignments, NOEs, and dipolar restraints for structure calculation. Access to the "magic field strength" of 900 MHz will allow us to best tackle molecular weight issues and also provide high resolution to overcome spectral degeneracy inherent in helical proteins. These studies will complement ongoing functional studies, provide mechanistic information relating to SLBP function, and test currently proposed models as to how the protein regulates histone protein synthesis in vivo. As yet no structural information exists on any of the regulators of histone metabolism, hence these studies will lay the groundwork for long term goals which are to understand how histone genes are post-transcriptionally regulated.
Project Details
Project type
Capability Research
Start Date
2005-10-01
End Date
2006-04-04
Status
Closed
Released Data Link
Team
Principal Investigator