Recruitment of the modified mRNA into retroviral particles. Quantitative RT-PCR analysis of luciferase-mRNA content extracted from retroviral particles produced in cells transfected with the packaging constructs and the test-constructs, 48 h post-transfection. All results were normalized for transfection-efficiency with GFP expression determined by FACS analysis. Comparisons were performed using Wilcoxon-Mann–Whitney analysis. NT: untransfected cells. Number of experiments, N = 3.