Cryoelectron microscopy and cryoelectron tomography of the nuclear pre-mRNA processing machine.
Large nuclear ribonucleoprotein particles, which can be viewed as the naturally assembled precursor messenger RNA (pre-mRNA) processing machine, were analyzed in frozen-hydrated preparations by cryoelectron microscopy. A general and reproducible strategy for preparing ice-embedded large nuclear ribonucleoprotein (lnRNP) particles at sufficiently high concentration was developed. Taking advantage of their negatively charged components, the lnRNP particles are adsorbed and thus concentrated on a positively charged lipid monolayer while preserving their native structure. Using this approach we carried out cryoelectron tomography and three-dimensional image reconstruction of individual lnRNP particles. The study revealed a structure similar to that of negatively stained particles studied previously, yet with additional features. The small additional domain visualized in negative stain appeared to be larger in the ice preparations. In addition, using image restoration from focus series of ice-embedded lnRNP particles, new features such as holes within the subunits were visualized in two dimensions, and it was shown that the subunits are interconnected via a fiber, very likely formed by the pre-mRNA. This finding supports the model that each subunit represents a spliceosome that splices out the intron wound around it.
Medalia
Ohad
O
Department of Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
Typke
Dieter
D
Hegerl
Reiner
R
Angenitzki
Mina
M
Sperling
Joseph
J
Sperling
Ruth
R
D022003:Cell Nucleus Structures / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D006367:HeLa Cells; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods; D008055:Lipids / Q000737:chemistry; D012322:RNA Precursors; D012323:RNA Processing, Post-Transcriptional; D012261:Ribonucleoproteins / Q000737:chemistry / Q000648:ultrastructure*; D017381:Spliceosomes; D014057:Tomography, X-Ray Computed
D008055:Lipids; D012322:RNA Precursors; D012261:Ribonucleoproteins