The many paths to frameshifting: kinetic modelling and analysis of the effects of different elongation steps on programmed-1 ribosomal frameshifting

Several important viruses including the human immunodeficiency virus type 1 (HIV-1) and the SARS-associated Coronavirus (SARS-CoV) employ programmed -1 ribosomal frameshifting (PRF) for their protein expression. Here, a kinetic framework is developed to describe -1 PRF. The model reveals three kinetic pathways to -1 PRF that yield two possible frameshift products: those incorporating zero frame encoded A-site tRNAs in the recoding site, and products incorporating -1 frame encoded A-site tRNAs. Using known kinetic rate constants, the individual contributions of different steps of the translation elongation cycle to -1 PRF and the ratio between two types of frameshift products were evaluated. A dual fluorescence reporter was employed in Escherichia coli to empirically test the model. Additionally, the study applied a novel mass spectrometry approach to quantify the ratios of the two frameshift products. A more detailed understanding of the mechanisms underlying -1 PRF may provide insight into developing antiviral therapeutics.