Structural studies on RNA processing factors
The expression of genetic information carried in the DNA of living cells involves two major steps, transcription and translation. In eukaryotes, the initial transcription products need to be further processed before they can serve as templates for protein synthesis. One such process is splicing, which selectively removes the introns and connects the coding sequences (exons). Splicing also deposits a multiprotein complex, the exon junction complex (EJC), at a position approximately 20 nucleotides upstream of exon exon junctions of spliced mRNA to facilitate post-splicing RNA processing. Among eight identified EJC components, transcription factor Aly/REF and splicing factor UAP56 have been shown to stimulate the export of both spliced and unspliced mRNA. They provide links between these cellular events. During the export, two other components, Y14 and Mago will accompany mRNA into the cytoplasm and maintain association with mRNA until the first round of translation. They are considered core proteins in EJC.
During the period of my study, I first crystallized and determined the structure of UAP56(Δ1–44) at 1.95 Å resolution by molecular replacement. The structure reveals that UAP56 belongs to the DEXD RNA helicase family and contains minimal helicase domains in an elongated shape similar to the well-studied protein eIF4A.
I then crystallized and determined the crystal structure of Drosophila Y14 (DmY14) RRM domain (a.a. 47–156) in complex with full-length Mago nashi (Mago) at 1.85 Å resolution. The structure shows that the strong interaction maintained between these two proteins is the result of hydrophobic interaction between the RNP motifs of Y14 and Mago. The structure implies that Y14 can not interact with RNA in a manner similar to other RRM-containing proteins. The stable association between Y14/Mago and mRNA is either bridged by unknown protein factors or requires a folding rearrangement.
0307: Molecular biology