Endogenous retrovirus group FH21 member 1 (ERVFH21-1), formerly HERV-F(XA34), is an integrated retroviral element of the human genome. It is known that human endogenous retroviruses (ERVs) and ERV-like sequences are part of the repetitive portions of the human genome and are remnants of infections of former exogenous retroviruses. They comprise approximately 8% of the human genome (Landers et al, 2001) and include solitary long terminal repeats (LTRs), non-retroviral sequences flanked by LTRs, and LTRs-like sequences (Mayer et al, 2011). ERVs are divided into various groups. ERVFH21-1 is member 1 of the group F/H of endogenous retroviruses and maps on Chromosome 7, in particular on 7p21.3 (Okahara et al, 2004).

Usually, human ERVs are silenced epigenetically and are not transcribed (Kewitz and Staege, 2013), however, they are found to be transcribed in particular situations, such as under pathological conditions, and usually their transcription is initiated by promoter sequences within the proviral LTRs (Mayer et al, 2011). An mRNA sequence for ERVFH21-1 is registered in GenBank as AK023847. The tissue of origin in which it has been identified is the placenta (Kjellman et al, 1999).

mRNA was detected in placenta (high expression), in saliva (low expression) (ref.: bioGPS.org), and in fetal tissues (Kjellman et al, 1999).

No pseudogenes were observed for the ERVFH21-1 sequence.

It is well-known that human ERVs and ERV-like sequences no longer encode proteins because of the accumulation of nonsense mutations as a consequence of their ancient incorporation into the genome of the host (Mayer et al, 2011). For ERVFH21-1 no protein has been identified so far.