Associate Professor
Department of Molecular Biology and Genetics
School of Medicine

ragreen@jhmi.edu

702A PCTB
725 N. Wolfe Street
Baltimore, MD 21205

Office: 410-614-4922
Lab: 410-614-4928

The ribosome is the two-subunit macromolecular complex responsible for the translation of the genetic code into functional polypeptides. The ribosome is composed of RNA (3 large rRNAs in bacteria) and protein (more than 50 r-proteins in bacteria) in a mass ratio of about 2 to 1. We are interested in understanding how this ribonucleoprotein machine catalyzes and coordinates the complex molecular events of translation. These studies may reveal important details that impact on the function of other RNP machines such as the spliceosome and telomerase and may uncover clues that help us to think about the early origins of life and the specifics of the 'RNA world'. Further, as ribosomes are the target of many clinically relevant anti-microbial agents (erythromycin, chloramphenicol, and aminoglycosides), there are modern day applications for drug development from what we learn in our basic studies.

The work in our laboratory focuses on a number of the different steps in the translation cycle including decoding, peptide bond formation, translocation and peptide release. Recent advances in X-ray crystallography have provided us with atomic resolution views of the large and small subunits of the ribosome. These views have revealed that the functional core of the ribosome is predominantly composed of RNA and has identified phylogenetically conserved regions of particular functional interest. We are interesting in understanding the molecular mechanism of translation with a particular challenge being to define the dynamics of this RNP machine during the multiple different events of the translation cycle. We use a variety of mutational approaches targeting the ribosome itself as well as the translation factors and tRNA and a set of well-defined pre-steady state assays to evaluate the contributions made by specific components to the function of this RNP machine. These pre-steady state assays involve rapid quench kinetics as well as fluorescence studies that follow the physical changes in the various components of the machinery. A current new project is focused on understanding the conformational rearrangements in the ribosome, the tRNAs and the release factors that are critical to the related downstream steps of peptidyl transfer and peptide release. From these types of studies, we hope to eventually compare the activities of RNA and protein enzymes reaching general conclusions regarding the strategies utilized by these different biopolymers to catalyze similar chemical reactions.

Selected Publications
Dorner, S., J.L. Brunelle, D. Sharma, and R. Green. (2006) The hybrid state of tRNA binding is an authentic translation elongation intermediate. Nat. Struct. Mol. Biol. 13:234-241.

Brunelle, J.L., E.M. Youngman, D. Sharma, and R. Green. (2006) The interaction between C75 of tRNA and the A loop of the ribosome stimulates peptidyl transferase activity. RNA 12:33-39.

Cochella, L., and R. Green. (2005) An active role for tRNA in decoding beyond codon:anticodon pairing. Science 308:1178-1180.

Cukras, A., and R. Green. (2005) Multiple effects of S13 in modulating the strength of intersubunit interactions in the ribosome during translation. J. Mol. Biol. 349:47-59.

Youngman, E.M., J.L. Brunelle, A.B. Kochaniak and R. Green. (2004) The active site of the ribosome is composed of two layers of conserved nucleotides with distinct roles in peptide bond formation and peptide release. Cell 117:589-99.

Merryman, C. and R. Green. (2004) Transformation of aminoacyl tRNAs for the in vitro selection of “drug-like” molecules. Chem. Biol. 11:575-82.

Cochella, L. and R. Green. (2004) Isolation of antibiotic resistance mutations in the rRNA by using an in vitro selection system. PNAS 101:3786-91.