Structure and function of Nopp140 and treacle

Abstract

Determining how individual nucleolar proteins regulate preribosomal RNA transcription, its processing (cleavage and chemical modifications) and association with ribosomal proteins in the assembly of small and large ribosomal subunits, and the final egress of these subunits to the cytoplasm remains a critical endeavor as we explore the primal cell function of ribosome biogenesis. Here, we review two proteins, nucleolar phosphoprotein of 140 kDa (Nopp140) and treacle, which share structural and functional similarities. We present Nopp140 first because of its earlier discovery and because Nopp140 is conserved throughout the eukaryotes. Conversely, treacle appears to be restricted to the vertebrates; thus, vertebrates express both Nopp140 and treacle. We describe what is currently known about their domain composition, their molecular associations, and how these associations suggest functions as chaperones for small nucleolar RNPs in pre-rRNA processing and as potential transcription factors for RNA polymerase I. We also describe cell stress responses (apoptosis) that result from the loss of these proteins in progenitor cells, thus leading to developmental abnormalities. This review is intended to spark new and imaginative research approaches toward investigating not only Nopp140 and treacle, but also the many other nucleolar proteins that facilitate ribosome biogenesis. © 2011 Springer Science+Business Media, LLC.