Type of mutations. Data are shown with respect to gene class 1 (common insertion sites, proto-oncogenes, and self-renewal genes), class 2 (signaling genes), and classes 3 and 4 (other and unknown genes). (A) Position of RVIS in the Insertional Dominance Database (IDDb) around the transcriptional start site. Reference data insertion sites of different vectors in freshly transduced cells, shown as lines, were kindly provided by G. Trobridge and D. Russell.⁴¹  MLV indicates murine leukemia virus vector; FV, foamy virus vector; HIV, human immunodeficiency virus vector; random, computer-predicted random insertion pattern. (B) Overrepresentation of enhancer mutations in class 1 genes. RVISs were analyzed for the different types of retroviral insertional mutations proposed earlier.¹²  Insertions located downstream but in an antisense orientation do not correspond to the definition of enhancer mutations suggested in Uren et al¹²  and are therefore labeled “Except. +/R.”.