Date of this Version
A NOVEL PROTEIN ARGININE METHYLTRANSFERASE INTERACTS WITH THE RNA INDUCED SILENCING COMPLEX COMPONENT, MUT70, AND IS REQUIRED FOR RNA INTERFERENCE IN CHLAMYDOMONAS REINHARTII
James Becker, M.S.
University of Nebraska, 2009
Advisor: Heriberto Cerutti
RNA interference (RNAi) is an important gene regulatory mechanism. It involves 21-24 nucleotide small RNA molecules that downregulate complementary, or near complementary, mRNA sequences through transcript degradation or translation repression. The non-coding small RNA molecules act through an effector complex known as the RNA induced silencing complex (RISC). The components of RISC are evolutionarily conserved and consist of DICER and AGO proteins as well as several other polypeptides. These include, among others, MUT70, an RNA binding protein that has an RGG rich domain. Protein arginine methyltransferases typically methylate RGG rich regions, affecting protein stability, localization, and/or interactions. Here, we report that Protein Arginine Methyltransferase 2 (PRMT2) is required for RNAi in the green algae Chlamydomonas reinhardtii. Phylogenetic analyses indicate that the PRMT2 protein likely evolved in the plant/algal lineage. Interestingly, PRMT2 depletion resulted in a defect in RNAi-mediated translational repression. Moreover, in vitro analyses showed that MUT70 and PRMT2 interact directly and that PRMT2 can methylate MUT70. A point mutation in a highly conserved region of the methyltransferase domain disrupted methylation activity, but increased the affinity of PRMT2 for the MUT70 substrate. Our results, taken together, indicate that PRMT2 is required for RNAi, presumably through its modification of the MUT70 RISC component. However, elucidating the precise mechanistic role of PRMT2 will require further exploration.