[citation needed] JSRV is transmitted by the respiratory route and may also infect lymphocytes and myeloid cells, in addition to the lung epithelia.

Expression of the JSRV Envelope protein activates signalling cascades that promote cellular proliferation and malignant transformation of the cells.

Initially, the tumour cells grow along the alveolar walls in a pattern reminiscent of human BAC, but subsequently become more invasive and metastasize to the local lymph nodes.

The entry of the JSRV core into the cytoplasm activates reverse transcription, during which the single-stranded RNA genome is converted into a double-stranded DNA form and gets integrated as a provirus into the host.

Following transcription and translation of the viral genome, the new progeny virus gets assembled at the plasma membrane and bud off from the host cell acquiring a lipid envelope and their "env" glycoproteins.

But JSRV is different in this aspect since its envelope glycoprotein ("env") by itself is an oncogene and this single protein was shown to be necessary and sufficient to induce lung tumors in sheep.

Thus oncogenic JSRV has borrowed features of both pH-dependent and pH-independent viruses for entry which involves both the receptor binding and a low pH for fusion transformation of host cells.

[2][9][10] An example of this protection is seen in ovine endometrial epithelium where the high expression of enJSVR prevents exogenous JSVR from entering the cells via blocking the common receptor to both, HYAL2.

Their expression coincides with the key events of conceptus elongation and onset of trophoblast giant binucleate cells (BNC) differentiation.

[11] Furthermore, it was observed that an injection of morpholinos (an enJSRV envelope production inhibitor) into the uteri of pregnant sheep on day 8 of pregnancy resulted in reduced conceptus elongation and inhibition of trophoblast giant BNC differentiation.

[11] Whilst the cellular and molecular mechanism are still unclear, it is apparent it has a role in protecting the uterus against viral infection and placental morphogenesis.

[8] Of interest for comparative physiology is that the presence of enJSRV envelope protein expression in the developing sheep placenta is very similar to that observed for syncytin in humans and the mouse.

[8] Research surrounding endogenous retroviruses supports the idea that they may play critical roles in conceptus growth, placental differentiation and cell fusion in mammals.