Retroviruses as genetic tools to isolate transcriptionally active chromosomal regions

By exploiting the ability of retroviruses to move genes into random sites of mammalian genomes and by exploiting some features of their replication, retrovirus vectors have been developed that select for instances in which the virus integrates into expressed genes. Since integrated proviruses tag transcriptionally active sites, the vectors provide a means to identify and isolate promoters active in different cell types. Furthermore, the viruses may be useful as insertional mutagens, since they select for instances in which integration occurs into expressed sites. This reduces the number of integrants needed to screen for loss of gene function and may enable genes controlling phenotypes in mammalian cells to be isolated.