STRUCTURAL STUDIES OF REGULATORS OF HISTONE PROTEIN SYNTHESIS
EMSL Project ID
25653
Abstract
STRUCTURAL STUDIES OF REGULATORS OF HISTONE PROTEIN SYNTHESIS. Roopa Thapar and William F. Marzluff In each cell cycle a eukaryotic cell must not only replicate its DNA, but must also synthesize sufficient new histone protein to package the newly replicated DNA into chromatin. In metazoans there is a unique set of genes, the replication dependent histone genes that encode the bulk of the histone mRNAs in metazoans. These mRNAs have a number of unique properties that set them apart from other eukaryotic mRNAs. The replication-dependent histone genes do not contain introns and the metazoan histone mRNAs are the only eukaryotic mRNAs that are not polyadenylated. The replication dependent histone mRNAs are cell-cycle regulated, and are highly expressed only during S-phase. The major cis-element responsible for the coordinate cell-cycle regulation of the histone mRNAs is the unique 3' end of histone mRNAs. In addition, the 3' end of histone mRNA must fulfill any essential functions on a histone mRNA that the polyA tail fulfills on other mRNAs. The stem-loop binding protein, SLBP binds to the stem-loop in the histone pre-mRNA. Three major functions of SLBP have been described: binding of the stem-loop RNA, stimulation of histone pre-mRNA processing by stabilizing U7 snRNP binding to the histone pre-mRNA, and stimulation of histone mRNA translation. Once bound to the histone mRNA stem-loop, SLBP helps recruit the multiprotein-RNA complex that is necessary for histone mRNA processing. It also interacts with translation initiation factors to enhance translation of histone mRNAs performing the function that PABP/polyA performs on other eukaryotic mRNAs. SLBP remains with the mRNA after processing and accompanies the processed mRNA to the cytoplasm. Substantial evidence indicates that the 3' end of histone mRNA is necessary for efficient translation in vivo. We have identified a novel protein, termed SLBP Interacting Protein or SLIP-1, using the yeast 2-hybrid system with SLBP as a bait. This protein interacts specifically with the translation activation region of SLBP, and stimulates translation in Xenopus oocytes. It is a novel protein containing an MIF4G domain (based upon sequence alignments) that is found in proteins with diverse functions in RNA metabolism. Based upon biological and biochemical studies (Marzluff lab, unpublished) our current model is that SLIP-1 forms a bridge between SLBP and the initiation complex at the 5' end of the mRNA. At present there is no structural information available for SLBP or SLIP1 or any of the other factors specific to histone protein synthesis. Recent in vitro evidence also suggests that SLIP1 may play a more general role, interacting with other factors of the translation and mRNA degradation machinery. These studies will therefore provide atomic level insight into how mRNAs are translated and degraded in the control of gene expression.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-06-01
End Date
2008-12-02
Status
Closed
Released Data Link
Team
Principal Investigator