RESUMO
Single molecule assays of splicing and spliceosome assembly can provide unique insights into pre-mRNA processing that complement other technologies. Key to these experiments is the fabrication of fluorescent molecules (pre-mRNAs and spliceosome components) and passivated glass slides for each experiment. Here we describe how to produce fluorescent RNAs by splinted RNA ligation and fluorescent spliceosome subunits by SNAP-tagging proteins in cell lysate. We then depict how to passivate glass slides with polyethylene glycol for use on an inverted microscope with objective-based total internal reflection fluorescence (TIRF) optics. Finally, we describe how to tether the pre-mRNA onto the passivated slide surface and introduce the SNAP-tagged cell lysate for analysis of spliceosome assembly by single molecule fluorescence.
Assuntos
Biologia Molecular/métodos , Splicing de RNA/genética , Spliceossomos/genética , Catálise , Extratos Celulares , Fluorescência , Precursores de RNA/genética , Saccharomyces cerevisiae , Spliceossomos/ultraestruturaRESUMO
The spliceosome is the complex macromolecular machine responsible for removing introns from precursors to messenger RNAs (pre-mRNAs). We combined yeast genetic engineering, chemical biology, and multiwavelength fluorescence microscopy to follow assembly of single spliceosomes in real time in whole-cell extracts. We find that individual spliceosomal subcomplexes associate with pre-mRNA sequentially via an ordered pathway to yield functional spliceosomes and that association of every subcomplex is reversible. Further, early subcomplex binding events do not fully commit a pre-mRNA to splicing; rather, commitment increases as assembly proceeds. These findings have important implications for the regulation of alternative splicing. This experimental strategy should prove widely useful for mechanistic analysis of other macromolecular machines in environments approaching the complexity of living cells.
