title: Forks in the tracks: Group II introns, spliceosomes, telomeres and beyond.
abstract: Group II introns are large catalytic RNAs that form a ribonucleoprotein (RNP) complex by binding to an intron-encoded protein (IEP). The IEP, which facilitates both RNA splicing and intron mobility, has multiple activities including reverse transcriptase. Recent structures of a group II intron RNP complex and of IEPs from diverse bacteria fuel arguments that group II introns are ancestrally related to eukaryotic spliceosomes as well as to telomerase and viruses. Furthermore, recent structural studies of various functional states of the spliceosome allow us to draw parallels between the group II intron RNP and the spliceosome. Here we present an overview of these studies, with an emphasis on the structure of the IEPs in their isolated and RNA-bound states and on their evolutionary relatedness. In addition, we address the conundrum of the free, albeit truncated IEPs forming dimers, whereas the IEP bound to the intron ribozyme is a monomer in the mature RNP. Future studies needed to resolve some of the outstanding issues related to group II intron RNP function and dynamics are also discussed.
authors.affiliation: a Laboratory of Cellular and Molecular Basis of Diseases, Division of Translational Medicine, Wadsworth Center , New York State Department of Health , Albany , NY , USA.|b Department of Biomedical Sciences, School of Public Health , University at Albany , Albany , NY , USA.
authors.forename: Rajendra Kumar
authors.initials: RK
authors.lastname: Agrawal
authors.affiliation: c Ministry of Education Key Laboratory of Protein Sciences , Tsinghua-Peking Joint Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University , Beijing , China.|d Department of Molecular Biophysics and Biochemistry , Yale University , New Haven , CT , USA.
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Wang
authors.affiliation: b Department of Biomedical Sciences, School of Public Health , University at Albany , Albany , NY , USA.|e Department of Biological Sciences and RNA Institute , University at Albany , Albany , NY , USA.
authors.forename: Marlene
authors.initials: M
authors.lastname: Belfort
mesh_terms: D019143:Evolution, Molecular; D008958:Models, Molecular; D008968:Molecular Conformation; D010802:Phylogeny; D016337:RNA, Catalytic / Q000737:chemistry / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism; D017381:Spliceosomes / Q000737:chemistry / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*
chemical_list: D016337:RNA, Catalytic; D012261:Ribonucleoproteins
keywords: Cryo-EM; Prp8; intron RNP structure; intron-encoded protein; reverse transcriptase; telomerase