FIG. 1.

Gene trap strategy with ROSA-nGBT vector. In the cells infected with this virus, the integrated proviral DNA became transcriptionally silent. The nGBT reporter gene lacks its own promoter but is preceded by a strong splice acceptor sequence. When the viral DNA is integrated in an active transcriptional unit in the host genome, the nGBT gene can be transcribed as a part of the chimeric mRNA whose 5′ portion is derived from the host transcript. SA, splice acceptor.