A REPLICATION-COMPETENT PROMOTER-TRAP RETROVIRUS

A promoter-trap retrovirus has been constructed in which a promoterles s polyomavirus middle T antigen gene was inserted in the U3 region of the long terminal repeat of a replication-competent Moloney murine leu kemia virus. The resulting vints, designated PyT, was used to infect m ouse mammary glands in situ. As expected, mammary tumors appeared in s ome infected animals. These tumors were found to contain PyT proviruse s of the predicted structure. From one such tumor, the PyT provirus an d surrounding sequences from the integration site were cloned. The pro virus was found to have integrated adjacent to the promoter of a novel mouse gene (TRAP1) that was expressed at low levels in various mouse tissues, These data show that the PyT retrovirus provides a sensitive means of detecting active promoters in vivo.