The translation of messenger RNA into the appropriate protein is a very fundamental process of cell growth. As a result, translation is closely tied to growth regulation pathways at many levels. The ribosome is an extremely intricate ribonucleoprotein complex that is capable of mRNA decoding, aminoacylation, and mRNA tRNA movement; all of which occurs in a very coordinated series of steps. Knowledge of the exact mechanism the ribosome uses to carry out each one of these steps is limited or non existent. The current research is focused on the elucidation of molecular interactions between ribosomes and tRNA that are necessary for decoding and translocation of the tRNA mRNA complex. My previous work has shown that the sequence independent 2 'OH portion of the ribose at specific positions in a tRNA analog (ASL) form hydrogen bonds with the ribosome at universally conserved rRNA residues. Additionally, these interactions were shown to be critical for ribosomal A site binding and translocation. Sequence independent phosphate oxygens of the RNA backbone of tRNA may also play an important role in A site binding and translocation. Currently, we are evaluating the effect phosphorothioate modified ASLs might have on the process of translocation.

The ribosome, tRNAs, mRNAs and its factors are all targets for cell growth regulation, and have been shown to be involved in pancreatic, breast, brain, and colon cancers. A well known example of translational regulation is the mitogenic activation of p53, which is responsible for the rapid dephosphorylation of required initiation factors as well as the inhibition of ribosomal protein S6 kinase. Inhibition of S6 kinase inhibits translation, but the exact mechanism by which this occurs is not known. An in depth analysis of the molecular interactions that are required for ribosomal translation will allow us to improve our understanding of how gene expression is controlled in a growing cell.

PUBLICATIONS (resulting from this training and some recent ones)

Phelps SS, Jerinic O, Joseph S. (2002) Universally conserved interactions between the ribosome and the anticodon stem-l oop of A site tRNA important for translocation. Mol Cell. 10:799-807.

Phelps SS, Malkiewicz A, Agris PF, Joseph S. (2004) Modified nucleotides in tRNA(Lys) and tRNA(Val) are important for translocation. J Mol Biol. 338:439-44.

Phelps SS, Joseph S. (2005) Non-bridging phosphate oxygen atoms within the tRNA anticodon stem-loop are esse ntial for ribosomal A site binding and translocation. J Mol Biol. 349:288-301.

Phelps SS, Gaudin C, Yoshizawa S, Benitez C, Fourmy D, Joseph S. (2006) Translocation of a tRNA with an extended anticodon through the ribosome. J Mol Biol. 360:610-22.

Komoda T, Sato NS, Phelps SS, Namba N, Joseph S, Suzuki T. (2006) The A-site finger in 23 S rRNA acts as a functional attenuator for translocation. J Biol Chem. 281:32303-9.

Dunham CM, Selmer M, Phelps SS, Kelley AC, Suzuki T, Joseph S, Ramakrishnan V. (2007) Structures of tRNAs with an expanded anticodon loop in the decoding center of the 30S ribosomal subunit. RNA. Apr 6; [Epub ahead of print]