Poster abstracts

Poster number 53 submitted by Jelena Jakovljevic

Roles played by ribosomal proteins in ribosome assembly

Jelena Jakovljevic, Michael Gamalinda (Department of Biological Sciences, Carnegie Mellon University), Lisa Alexander, Aarti Sahasranaman (Department of Biological Sciences, Carnegie Mellon University), Jason Talkish (Department of Biological Sciences, Carnegie Mellon University), Philipp Milkereit (Institut für Biochemie III, Universität Regensburg), Reyes Babiano, Jesus de la Cruz (Departamento de Genetica, Universidad de Sevilla), John Woolford (Department of Biological Sciences, Carnegie Mellon University)

Abstract:
Ribosomes have elaborate structures composed of ribosomal proteins embellished in a core of ribosomal RNA (rRNA). We are interested in how these ribonucleoprotein complexes are assembled. Ribosome biogenesis is a tightly controlled process involving a series of intertwined events: processing and modification of the rRNA primary transcript, hierarchical and cooperative assembly of ribosomal proteins, and remodeling of preribosome (pre-rRNP) conformations to ultimately form mature functional ribosomes. We study the molecular mechanisms governing the formation of the large ribosomal subunit. Assembly of the 60S subunit is precisely coordinated - starting in the nucleolus and finishing in the cytoplasm. Each step is mediated by trans-acting assembly factors that transiently associate with preribosomes. Thus far, most studies on ribosome assembly have focused on characterizing how the absence of or mutations in assembly factors affect the assembly pathway. In contrast, although most ribosomal proteins are crucial to the formation of properly functioning ribosomes, very little is known about their role in the biogenesis pathway. We and others have recently tested how in vivo depletion of each ribosomal protein affects ribosome assembly and found that the absence of individual ribosomal proteins leads to defects in distinct pre-rRNA processing steps. Of the thirty-one large subunit ribosomal proteins (rpLs) tested, nine specifically affect processing of 27SA to 27SB pre-rRNA, seven affect processing of 27SB to 7S and 25.5S pre-rRNAs, and eight affect conversion of 7S pre-rRNA to 5.8S mature RNA. Our lab is particularly interested in the 27A₃ and 27B pre-rRNA processing steps; thus we started to characterize in further detail the roles of each rpL affecting these events. We investigated the effects of rpL depletion on pre-rRNA processing, association of assembly factors and other rpLs with preribosomes, and export of pre-rRNAs from nucleus to cytoplasm.

References:
Ferreira-Cerca, S., Pöll, G., Kühn, H., Neueder, A., Jakob, S., Tschochner, H., and Milkereit, P. (2007) Analysis of the in vivo assembly pathway of eukaryotic 40S ribosomal proteins. Mol Cell. 28: 446-457.
O’Donohue, M.F., Choesmel, V., Faubladier, M., Fichant, G., and Gleizes, P.E. (2010) Functional dichotomy of ribosomal proteins during the synthesis of mammalian 40S ribosomal subunits. J. Cell. Biol. 190:5 853–866.

Pöll, G., Braun, T., Jakovljevic, J., Neueder, A., Jakob, S., Woolford, J.L., Jr., Tschochner, H., Milkereit, P. (2009) rRNA maturation in yeast cells depleted of large ribosomal subunit proteins. PLoS One. 4:e8249. doi:10.1371/journal.pone.0008249.

Keywords: ribosome assembly, ribosomal proteins, pre-rRNA processing