Fig. 1. Effect of SD′ mutation on virus replication in vector production system and trans-complementation assay. (A) Schematic maps of plasmids used in the virus vector production system and expressing the viral components independently. Location of splice donor (SD) and acceptor (SA) sites is shown. Mutations are indicated by asterisks and inactivated functions are crossed. The two versions of the genomic vector are represented: wt, wild type; mutant, inactivated SD′ site (referred to F1 mutation; Dejardin et al., 2000). (B) Structure of plasmid allowing prespliced SD′ RNA and used in trans-complementation assays. (C) Titration of virus stocks on NIH3T3 target cells. The vector pseudotypes of retroviruses shared common capsid and envelope proteins; only the nature of the genomic vector varied. In trans-complementation assays, the additional vector is noted as +SD′ for the p57cDNASD′ vector. Titers are given in AP focus-forming units per milliliter. Experiments were performed at least three times for each virus in parallel and each test was performed in quadruple. The bars indicate the standard error of the mean of each series.