Electron microscopy of assembly intermediates of the snRNP core: morphological similarities between the RNA-free (E.F.G) protein heteromer and the intact snRNP core.

摘要: Abstract All four spliceosomal small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/U6 and U5 contain a common structural element called the snRNP core. This core is assembled from proteins RNA (snRNA). We have used electron microscopy to study structure of two intermediates assembly pathway: (1) (E.F.G) protein complex, which contains only smallest E, F G; (2) subscore snRNP, in D1 D2 are bound complex. The general was found resemble that complete core, components plus B/B′ D3. Both particles globular, with diameters 7 8 nm. They show characteristic accumulation stain at centre. However, some images showed nicked outlines not seen cores. complex appeared as ring, an outer diameter about nm central hole 2 across. molecular dimensions G imply thickness ring Comparison subcore structures implicates flat side ring-shaped provides site(s) for other during assembly: first (and probably snRNA) formation, then D3 completion particle.