RNA



Purification and characterization of native spliceosomes suitable for three-dimensional structural analysis


MELISSA S.  JURICA  a1, LAWRENCE J.  LICKLIDER  a2, STEVEN P.  GYGI  a2, NIKOLAUS  GRIGORIEFF  a1 and MELISSA J.  MOORE  a1 c1
a1 Howard Hughes Medical Institute, Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454, USA
a2 Taplin Biological Mass Spectrometry Facility, Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA

Abstract

We describe characterization of spliceosomes affinity purified under native conditions. These spliceosomes consist largely of C complex containing splicing intermediates. After C complex assembly on an MS2 affinity-tagged pre-mRNA substrate containing a 3′ splice site mutation, followed by RNase H digestion of earlier complexes, spliceosomes were purified by size exclusion and affinity selection. This protocol yielded 40S C complexes in sufficient quantities to visualize in negative stain by electron microscopy. Complexes purified in this way contain U2, U5, and U6 snRNAs, but very little U1 or U4 snRNA. Analysis by tandem mass spectrometry confirmed the presence of core snRNP proteins (SM and LSM), U2 and U5 snRNP-specific proteins, and the second step factors Prp16, Prp17, Slu7, and Prp22. In contrast, proteins specific to earlier splicing complexes, such as U2AF and U1 snRNP components, were not detected in C complex, but were present in similarly purified H complex. Images of these spliceosomes revealed single particles with dimensions of approximately 270 × 240 [Angstrom capital A, ring] that assort into well-defined classes. These images represent an important first step toward attaining a comprehensive three-dimensional understanding of pre-mRNA splicing.

(Received January 2 2002)
(Accepted January 23 2002)


Key Words: electron microscopy; mass spectroscopy; pre-mRNA splicing; spliceosomes.

Correspondence:
c1 Reprint requests to: Melissa J. Moore, Howard Hughes Medical Institute, Brandeis University, Biochemistry Department, 415 South Street, Waltham, Massachusetts 02454, USA; e-mail: mmoore@brandeis.edu.