(737b) A Kinetic Model Reveals the Effects of the Different Steps of the Translation Elongation Cycle on -1 Programmed Ribosomal Frameshifting

Programmed ribosomal frameshifting (PRF) is the process by which ribosomes produce two different polypeptides from the same mRNA. In -1 PRF, stimulatory signals cause the ribosome to slip one nucleotide toward 5' end. In this study, we kinetically model -1 PRF through either incomplete translocation, or by slippage of P-site and A-site tRNAs either during or immediately after aa-tRNA accommodation. These models yield two possible -1 frameshift products: those incorporating zero frame A-site tRNA in the recoding site and products incorporating -1 frame A-site tRNA in the recoding site. Using known kinetic rate constants, we can determine the individual contributions of rates of translocation, GTP hydrolysis by elongation factors, and peptidyltransfer to -1 PRF. The modeling results are consistent with previous experimental observations. In addition, the model predicts that changes in the rate constants for each of these different steps can affect the ratio between two frameshift products. A dual fluorescence reporter system is currently being employed in Escherichia coli to empirically test the model.