May possess a function in tumorigenesis. When overexpressed. Protein expressed at very low level. This Np9 protein is encoded by a human specific provirus. Has a type 1 genome. The HERV-K(HML-2) family contains type 1 and type 2 genomes depending on the absence or presence of 292 nucleotides at the 5'-end of the env gene. Np9 proteins are translated from a doubly spliced transcript expressed exclusively by HERV-K(HML-2) type 1 proviral genomes. Np9 proteins share 14 N-terminal amino acids with HERV-K(HML-2) type 2 envelope proteins. The rest of the protein is encoded by a small exon located at the 3' end of the envelope gene. This exon shares the same splice acceptor site and therefore overlaps HERV-K(HML-2) type 2 Rec protein second exon. It is yet translated from an alternate reading frame.