Areas of Research
Posttranscriptional Regulation of Gene Expression in Parasitic Protozoa
In our laboratory we study the eukaryotic parasite Trypanosoma brucei, which is the causative agent of human African trypanosomiasis, also known as African sleeping sickness. This disease is invariably fatal if not treated, and current drugs are toxic and difficult to administer, and resistance is developing. Essential and novel processes in this parasite may serve as starting platforms for new drug therapies. In addition to being of great medical and economic importance, T. brucei is also an excellent model system for the study of posttranscriptional gene regulation, because regulation at the level of transcription is essentially absent in this organism. The primary focus of our laboratory is on the mechanisms and regulation of two RNA processing events in T. brucei: RNA editing and RNA turnover. A third related area of research is the mechanism by which posttranslational modification of RNA binding proteins by arginine methylation modulates RNA processing, stability, and translation. Our laboratory combines biochemical, genetic, genomic, and proteomic approaches towards understanding gene regulation and protein modification in this pathogenic eukaryote.
RNA editing is a novel mechanism for regulating gene expression in which sequence information is added to mRNAs after transcription by specific insertion and deletion of uridine residues. Editing generates translatable messages by creating the open reading frames as well as proper initiation and termination signals. The phenomenon is of fundamental importance in understanding how genetic information can be stored and processed, and it is an essential process in trypanosomes. We are currently performing functional and biochemical characterization of a large, dynamic RNA-protein complex termed the MRB1 (mitochondrial RNA binding 1) complex that is essential for RNA editing in Trypanosoma brucei. We are also analyzing how MRB1 links RNA editing to other mitochondrial gene regulatory processes.
Trypanosomes and their relatives are unique in that they essentially lack regulation of RNA polymerase II catalyzed transcription. Instead, gene regulation is effected primarily at the levels of RNA stability and translational control. We are currently focused on the function of an RNA binding protein, DRBD18, which we showed by RNAseq functions in both RNA stabilization and RNA destabilization, depending on the class of mRNA. Our current data support a model in which posttranslational modification of DRBD18 by arginine methylation impacts the stabilization vs. destabilization functions of this protein by regulating specific protein-protein and protein-RNA interactions. We are currently testing this model in vitro and in vivo using reporter assays, in vivo protein-RNA cross-linking, and protein-protein interaction assays.
Protein arginine methylation:
Methylation of arginine residues in proteins is a posttranslational modification whose importance in areas such as signal transduction, RNA trafficking, RNA processing, and transcription has recently become apparent. Interestingly, a very large percentage of proteins that undergo arginine methylation are RNA binding proteins. We have identified and characterized four protein arginine methyltransferases (PRMTs) that catalyze this process in T. brucei. We have also performed a global proteomic analysis of the arginine methylome of T. brucei, identifying >1100 methylproteins spanning most cellular compartments and a wide array of functional classes. We are currently analyzing novel mechanisms of PRMT regulation and defining the physiological and molecular functions of arginine methylmarks on selected proteins.