Structure and dynamics of the post-transcriptional mRNA-processing machinery

Eukaryotic gene expression depends on the synthesis, processing, export and translation of mRNA. These minisymposia tackled multiple aspects of the post-transcriptional pathway of mRNAs including the structure and dynamics of proteins implicated in splicing, polyadenylation and nuclear export.It has been known for some time that the mammalian cell nucleus contains numerous subcompartments, or bodies, which have been implicated in essential processes such as transcription and RNA processing. Cytological studies in which researchers observed the localization of various nuclear proteins have led to the definition of distinct nuclear subcompartments: the nucleolus, the nuclear speckles and several small nuclear bodies including the Cajal bodies (also called coiled bodies). An emerging theme of the meeting was the realization that these nuclear subcompartments are extremely dynamic and that proteins that are usually localized within these compartments are in fact moving rapidly throughout the entire nucleus. Highlights of these minisymposia included reports on the dynamics of proteins localized in these nuclear compartments from Tom Misteli (National Cancer Institute, National Institutes of Health, Bethesda, USA) and the biochemical purification of nucleoli and Cajal bodies from Angus Lamond (University of Dundee, UK).Using photobleaching techniques, Misteli and co-workers have shown that the vast majority of proteins move within the nucleoplasm by a passive, energy-independent mechanism. Photobleaching experiments have been used for many years to measure the mobility of proteins within lipid bilayers. Misteli and co-workers applied the method to analyze the mobility of proteins in the nucleus of living cells. In these experiments, a small area in the nucleus of a living cell that expresses a protein fused to green fluorescent protein (GFP) is bleached with a short, targeted laser pulse (Figure 1). The recovery of the fluorescent signal in the bleached area as the conseq