报告摘要：Guide RNAs are a large class of non-coding RNAs that provide specificity to various biochemical reactions, including RNA modification, editing and cleavage. Guide RNAs recognize substrate RNAs by basepairing with complementary sequences in substrate RNA and present the target site for catalysis carried out by a protein enzyme. H/ACA guide RNAs associated with four proteins direct the site specific formation of pseudouridine in ribosomal RNAs and snRNA. We have determined the crystal structures of a fully assembled substrate-free H/ACA RNP and a substrate-bound complex. These structures reveal the organization of H/ACA RNP and show how the guide RNA directs site-specific modification of substrate. I will also talk about the interaction of RNA silencing suppressor P19 and siRNA duplex.