This short protein has no known function and is found in Jaagsiekte sheep retrovirus. Jaagsiekte sheep retrovirus (JSRV) is the etiological agent of a contagious lung tumour of sheep known as sheep pulmonary adenomatosis. JSRV exhibits a simple genetic organisation, characteristic of the type D and type B retroviruses, with the canonical retroviral sequences gag, pro, pol and env encoding the structural proteins of the virion. An additional open reading frame (orf-x), of approximately 500 bp overlapping pol [1].

1: An accessory open reading frame (orf-x) of jaagsiekte sheep retrovirus is conserved between different virus isolates. Rosati S, Pittau M, Alberti A, Pozzi S, York DF, Sharp JM, Palmarini M; Virus Res 2000;66:109-116. PMID:10653922