Poster abstracts

Poster number 116 submitted by Jared Schrader

Translational Control of the Caulobacter Cell Cycle

Jared Schrader (Biological Sciences, Wayne State University), Gene-Wei Li (Cellular and Molecular Pharmacology, UCSF), Bo Zhou (Develepmental Biology, Stanford University), Keren Lasker (Developmental Biology, Stanford University), Jonathan Weissman (Cellular and Molecular Pharmacology, UCSF), Lucy Shapiro (Developmental Biology, Stanford University)

Abstract:
Cellular differentiation is an essential process by which cells carrying identical genes develop into specialized cell types with distinct functions. An important goal in understanding cellular differentiation is to determine how the genetic information encoded in the genome is expressed properly in time and space to ensure the correct cell fate. The bacterium Caulobacter crescentus has proven to be an excellent model organism for studying cellular differentiation processes that occur as a function of the cell cycle. In Caulobacter each cell division is asymmetric, yielding a daughter with a different cell fate. This process requires rapid and specific changes in gene expression during the cell cycle that are controlled at many levels, including transcriptional regulation, transient DNA methylation, differential proteolysis, and protein phospho-signaling. However, relatively little is known about the cell cycle control of mRNA translation.

To understand the role of translational control in the Caulobacter cell cycle we employed ribosome profiling to monitor genome-wide changes in translation throughout the cell cycle. In agreement with data in E. coli and B. subtilis, ribosomes were observed to pause at internal Shine-Dalgarno (SD) sites within the coding sequence. Despite an identical anti-SD sequence of the ribosomal RNA across virtually all bacteria, only half of bacterial genes contain SDsites preceding start codons, including some genomes such as Caulobacter with very poor usage of this sequence. Therefore, the role of the SD is pausing may be the conserved function of this sequence and not translation initiation. While most cell cycle-regulated mRNAs are predominantly controlled at the transcription level, approximately 47% of cell cycle-regulated mRNAs are additionally regulated at the level of translation, including 56 mRNAs whose cell cycle-regulated expression is exclusively regulated at the level of translation. Genes undergoing cell cycle-regulated translational control include many critical genes involved in polar morphogenesis and cell cycle progression. Overall, our data shows that translational control provides an additional layer of regulation of the Caulobacter cell cycle and that this control is largely used to optimally tune the timing of gene expression.

Keywords: Translational Control, Ribosomes, bacteria