Molecular Study of Drosophila Gemin5

Small nuclear ribonucleoprotein particle (snRNP) is a multimeric RNA-protein complex that functions in RNA processing to produce messenger RNA for the production of protein in eukaryotes. The snRNP biogenesis is a multi-step process that is modulated by the protein machinery called the Survival of Motor Neuron (SMN) complex. Reduced levels or loss-of-function of SMN results Spinal Muscular Atrophy (SMA), a leading autosomal recessive disease that causes childhood mortality. The SMN complex contains SMN and eight additional proteins named Gemin2-8 and unrip. Previously, we have identified Gemin5 as the RNA binding protein that recognizes the UsnRNA, the major components of snRNP. Although the best characterized function of the SMN complex is snRNP processing, several lines of evidences indicated that it involves in other ribonucleoprotein (RNP) biogenesis. Recently, we demonstrated that the homologous gene of Gemin5 in fruit fly, rigor mortis (Rig), binds to UsnRNA with high affinity and specificity, and reduced level of Rig impairs the snRNP biogenesis. Rig was firstly identified to function in larval development of fruit fly, and was enriched with the SMN protein in the specific organelles called U bodies. U bodies are the processing and storage sites of UsnRNAs and invariably associated with another discrete domain called P bodies, the RNA granules for messenger RNA degradation, gene silencing and translational repression. In addition to show the similar RNA binding activities of Rig to human Gemin5, we further identified a novel class of RNA, transfer RNA (tRNA), that interacts with Rig using high-throughput sequencing and demonstrated that the Rig/tRNA interaction is direct and specific. Transfer RNAs are the major components of protein synthesis, and involves in stress-induced gene regulatory pathways. Therefore, we hypothesized that Rig and the SMN complex play roles in the crosstalk between U bodies and P bodies. In this proposal, the major questions that we plan to address is how Rig interacts with its RNA and protein partners as Gemin5, and what are the significances of Rig in the context of U/P bodies biogenesis during stress. To address this, we will focus on the biochemical characterization of Rig, and the study of Rig and SMN complexes in fruit fly. We believe that our findings will provide further understanding of Rig and the SMN complex in other RNP biogenesis pathways, and may shed light in the alternative pathogenic mechanism of SMA.