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Albany 2015:Book of Abstracts

Albany 2015
Conversation 19
June 9-13 2015
©Adenine Press (2012)

Structural dynamics of a mobile group II intron ribonucleoprotein complex

Group II introns are of interest not only because they are ribozymes that catalyze their own splicing, but also because they are evolutionarily related to spliceosomes, spliceosomal introns and retrotransposons. Spliceosomal introns and retrotransposons comprise over 50% of the human genome and are believed to be important in genome sculpting and stability. Group II introns are mobile genetic elements that behave like retrotransposons in targeting specific DNA homing sites (retrohoming) or ectopic sites (retrotransposition). In the cell, the introns associate with an intron-encoded protein (IEP) to form ribonucleoprotein (RNP) complexes. The assembly of precursor RNA with the IEP precedes RNA splicing, which can be followed by intron integration into target DNAs. Conformational changes accompany these transitions. The IEP participates in intron RNA folding and promotes splicing, besides being required for the early steps of DNA targeting in vivo. Crystal structures of in vitro-transcribed group II intron RNAs have been resolved, providing a basis to understand the mechanism of splicing. However, there is no structure of an IEP or of a native, active group II intron RNP complex. To better understand group II intron splicing and DNA targeting, we are capturing conformational changes between states. For this, we developed a two-step intein-based strategy to purify active group II intron RNP complexes in different states from the intron's native host Lactococcus lactis. Earlier studies using sedimentation, chromatography, cryo-EM and SAXS techniques captured some of these transitions at low resolution (Huang, T. et al, 2010; Gupta K. et al, 2014). We have now achieved a 5.3 Å resolution structure of this native group II intron RNP complex by cryo-EM and are starting to visualize structural details of the RNP and its components.

References
    Huang, T. et al. (2011). The group II intron ribonucleoprotein precursor is a large, loosely packed structure. Nucleic Acids Res 39, 2845-54.

    Gupta, K. et al. (2014). Quaternary arrangement of an active, native group II intron ribonucleoprotein complex revealed by small-angle X-ray scattering. Nucleic Acids Res 42, 5347-5360.


Guosheng Qu 1
Xiaolong Dong1
Carol Lyn Piazza1
Jia Wang2
Hongwei Wang2
Marlene Belfort1

1Department of Biological Sciences
RNA Institute
University at Albany
Albany, NY 12222
2School of Life Sciences
Tsinghua University
Beijing, China 100084

gqu@albany.edu