t.preiss@victorchang.unsw.edu.au

There is one space available for an Honours student to work on one of the projects outlined below.

Translational Control of Gene Expression

mRNA translation is an intricate and tightly controlled step in gene expression. It takes place on the ribosome and is aided by numerous accessory factors. The initiation phase of translation represents all processes required for the assembly of a complete (80S) ribosome, consisting of the small (40S) and large (60S) subunit, at the start codon of the mRNA. The 5’ cap structure and the 3’ poly(A) tail of a typical eukaryotic mRNA, through their respective binding proteins eIF4E and PABP, are of central importance during initiation. The adapter protein eIF4G interacts with both, eIF4E and PABP, bringing together the ends of the mRNA. Furthermore, eIF4G recruits the RNA helicase eIF4A as well as the 40S ribosomal subunit and associated initiation factors. Initiation and the functions of eIF4G and its interaction partners are frequent targets of regulatory intervention, which is important for normal cellular physiology as well as in a variety of disease states.

Selected References (Available on request)

• Preiss T, Hentze MW. Dual function of the messenger RNA cap structure in poly(A)-tail-promoted translation in yeast. Nature 1998; 392:516-520.

• De Gregorio E, Preiss T, Hentze MW. Translation driven by an eIF4G core domain in vivo. EMBO J 1999; 18:4865-4874.

• Preiss T, Hentze MW. Starting the protein synthesis machine: eukaryotic translation initiation. BioEssays 2003; 25(12):1201-11.

We study the mechanisms of initiating translation in yeast and mammalian cells using a combination of contemporary biochemical and genomic tools, including microarray technology. Honours student may select from projects within two broad areas of interest.

Program 1:  Gene expression and the adenylation state of the yeast transcriptome

Cells can alter the synthesis rate of individual proteins by changing the amount of the corresponding mRNA template and/or altering the efficiency with which ribosomes use these templates. For individual examples of mRNAs, it is well established that the poly(A) tail and mechanisms that control its length contribute to both types of change through its involvement in mRNA decay as well as -translation. To understand how the poly(A) tail and its length control contributes to gene regulation on a genome-wide level, we fractionate cellular mRNA based on poly(A) tail length using thermal elution from poly(U) sepharose. Microarray comparisons of mRNA pools with short and long poly(A) tails have allowed us to determine the adenylation state of the transcriptome and to identify hitherto unappreciated control of gene expression through specific mRNA deadenylation. In current work, we use a panel of mutant strains to define the source of the observed poly(A) length control.

Selected References (Available on request)

• Preiss T, Baron-Benhamou J, Ansorge W, Hentze MW. Homodirectional changes in transcriptome composition and translation induced by Rapamycin and heat shock. Nat Struct Biol 2003; 10(12):1039-47.

• Beilharz TH, Preiss T. Translational profiling: the genome-wide measure of the nascent proteome. Brief Funct Genomic Proteomic. 2004;3:103-11.

Program 2:  microRNA-mediated control of translation in mammalian cells

Reports over the last years have uncovered a previously hidden network of translational controls that is underpinned by hundreds of endogenously encoded, ~22-nt regulatory RNA molecules termed microRNAs. In animals, microRNAs often do not direct the degradation of mRNAs, but instead are thought to bind partially mismatched target sequences in the 3’ untranslated region of mRNAs and down-regulate their translation. Until very recently, it was not known how microRNAs bring about translational repression. We, and others then found that they affect the initiation phase of translation and we now investigate which sub-step is targeted and what (protein) factors mediate repression using cell culture models and an in vitro translation system. The mRNA targets for most microRNAs are currently not known, making bioinformatic target prediction another major focus of current microRNA research. To complement such efforts, we have devised several experimental approaches based on the use of microarrays to identify microRNA targets.

Selected Reference (Available on request)

• Humphreys DT, Westman BJ, Martin DI, Preiss T. MicroRNAs control translation initiation by inhibiting eukaryotic initiation factor 4E/cap and poly(A) tail function. Proc Natl Acad Sci U S A. 2005 Nov 22;102(47):16961-6.