A molecular scaffold that mediates box C/D snoRNP biogenesis

Individual functions in the cell are harnessed and controlled, often within large molecular machines. Examples include the activities that replicate DNA, synthesise proteins and generate RNA. Correct assembly of these machines is performed in a controlled way, far from their site of function. This is important as partially or incorrectly assembled complexes are likely to interfere with the normal processes in the cell. We wish to study the assembly of one family of such cellular machines, the box C/D snoRNPs, complexes that are important for the production of the machinery that produces proteins in the cell. Our aim is to study the role of assembly factors in the formation of the box C/D snoRNPs.

Structural, non-coding RNAs (ncRNAs) perform essential roles in almost all aspects of gene expression. They function as stable RNA-protein complexes, known as ribonucleoproteins (ncRNPs) that are often assembled in the cell at locations separate from their site of function. The biogenesis of ncRNPs has several common underlying themes which include: 1) assembly of the ncRNA into a precursor complex (pre-ncRNP) which aids or directs the binding of the ncRNP proteins. 2) processing the ncRNA. This includes either the removal of extra sequences at the 3' and/or 5' ends or modification of the nucleotides. 3) association of transport/localisation factors with the pre-ncRNP. Recent work indicates that all of these activities are co-ordinated and in several cases form part of a multifunctional and dynamic pre-ncRNP complex. However, the underlying principles of this process are poorly understood. Using the box C/D small nucleolar RNPs (snoRNPs / essential for ribosome biogenesis) as an example, we propose to study the co-ordination of distinct activities integral to ncRNP biogenesis. Our previous data has shown that activities responsible for assembly, localisation and RNA processing are present in a large, dynamic pre-snoRNP complex. Furthermore, the recruitment and function of these activities is highly regulated. In this current work we propose to investigate the formation of the pre-snoRNP complex and to analyse how this co-ordinates the assembly of the snoRNP and the recruitment of the RNA processing machinery.