Fig. 1.

Functional genes encoded by HERVs, on the example of HERV-K (HML-2) elements. a Genomic organization of the reconstituted full-size provirus. Apart from “classical” retroviral genes Gag, Prot, Pol and Env, an additional gene Rec or Np9, depending on the provirus type, is encoded. b Different types of proviral transcripts. Full-length subgenomic transcript encodes for Gag–Prot–Pol polyprotein, single-spliced product codes Envelope protein, double-spliced RNA is for Rec/Np9, whereas ~1.5 kb long completely spliced transcript of unknown function appears to lack any functional open reading frames