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. Author manuscript; available in PMC: 2024 Mar 6.
Published in final edited form as: Curr Opin Genet Dev. 2023 Jul 11;81:102086. doi: 10.1016/j.gde.2023.102086

Figure 1. Schematics of Retroviral Class Elements in Humans:

Figure 1

A) (Upper) A typical Human Endogenous Retrovirus (HERV) including (from left to right): Target Site Duplication (TSD), Long Terminal Repeat (LTR), a proviral genome with gag, pro, pol and env genes (Lower) A schematic of the LTR and it’s regulatory regions. Solo LTRs are highly related to those found in the provirus. B) (Top) Long Interspersed Nuclear Element (LINE) containing 2 open reading frames in the sense orientation and one in the anti-sense orientation. (Middle) A Small Interspersed Nuclear Element (SINE), a non-autonomous element which is reliant on LINE activity for mobility. The Alu element is a subfamily of SINEs and is nonautonomous but remains mobile in the human genome. (Bottom) The SINE-VTNR (Variable Number of Tandem Repeat)-Alu (SVA) element, which contains a SINE core repeat, and Alu-like region (antisense to the remainder of the element), a VNTR repetitive region and a SINE-R region, which is derived from HERVK10 and contains homology to LTR5Hs. C) Modes of cis-regulatory TE activity showing (Upper) enhancer activity where H3K27ac-marked TEs are bound by transcription factors (Middle) Promoter-acting TE, where an upstream integrant acts as a promoter for a downstream gene. (Lower) A TE acting as a 3D genome regulatory element.