Quantitative effect of suboptimal codon usage on translational efficiency of mRNA encoding HIV-1 Gag in intact T cells

Abstract

Background: The sequences of wild-isolate strains of Human Immunodeficiency Virus-1 (HIV-1) are characterized by low GC content and suboptimal codon usage. Codon optimization of DNA vectors can enhance protein expression both by enhancing translational efficiency, and altering RNA stability and export. Although gag codon optimization is widely used in DNA vectors and experimental vaccines, the actual effect of altered codon usage on gag translational efficieny has not been quantified. Methodology and Principal Findings: To quantify translational efficiency of gag mRNA in live T cells, we transfected Jurkat cells with increasing doses of capped, polyadenylated synthetic mRNA corresponding to wildtype or codon-optimized gag sequences, measured Gag production by quantitative ELISA and flow cytometry, and estimated the translational efficiency of each transcript as pg of Gag antigen produced per μg of input mRNA. We found that codon optimization yielded a small increase in gag translational efficieny (approximately 1.6 fold). In contrast when cells were transfected with DNA vectors requiring nuclear transcription and processing of gag mRNA, codon optimization resulted in a very large enhancement of Gag production. Conclusions: We conclude that suboptimal codon usage by HIV-1 results in only a slight loss of gag translational efficiency perse, with the vast majority of enhancement in protein expression from DNA vectors due to altered processing and export of nuclear RNA. Copyright: © 2008 Ngumbela et al.