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Human Endogenous Retrovirus-W is the coding for a protein that would normally be part of the envelope of one family of Human Endogenous Retro-Viruses, or HERVs.
HERV-W encoding sequences makes up about 1% of the human genome and are part of a superfamily of repetitive and transposable elements. There are 31 different families of HERVs that together make up about 8% of the human genome, this is four times more DNA than is devoted to protein coding genes.
Most HERVs in the genome today are not replication-competent due to frame shifts, premature stop codons and recombination in their long terminal repeats. Each HERV family is derived from a single infection of the germline by an exogenous retrovirus that, once integrated, expanded and evolved. A complete HERV contains U3RU5- gag- pro- pol- env –U3RU5, where U3RU5 are long terminal repeats and gag, pro, pol and env are genes.