Fig. 2.

Long interspersed element 1 (L1) and endogenous retrovirus (ERV) regulatory impact post-integration. Most L1 copies are 5′ truncated (left) and lack the sense and antisense L1 promoters located in the 5′ untranslated region (large blue box). As a result, these L1 insertions have less capacity to drive chimeric transcription with neighboring genes. ERV insertions (right) remain either full-length, with flanking 5′ (black box) and 3′ long terminal repeats (LTRs; red box) that potentially retain promoter function, or, more commonly, recombine between the LTRs to form a solitary LTR, which retains the promoter/enhancer region. Arrows indicate putative transcription start sites