Splicing stories and poly(A) tales: an update on RNA processing and transport.

The basic steps in RNA processing, transport and translation have been conserved throughout eukaryotic evolution, as have many of the components involved. Nevertheless, the recognition processes which underlie RNA metabolism also display non-conserved features, whose appearance may have been made necessary by the increasing number and variety of processing substrates in higher eukaryotes and the complex requirements for differential regulation of RNA metabolism. Although many components of the mRNA processing machinery have been identified, our understanding of how a precursor is defined and accurately processed is still rudimentary. There are numerous indications that gene expression, from transcription all the way through to translation, is an integrated process. The challenge is to understand RNA processing and transport within this integrated whole.