structural:expansion, linguistic:paraphrasing, information:classification, structural:reformatting, structural:scholar_edition
Structure and genome

However, not all RSV strains have all four genes that allow it to both replicate on its own and cause transformation. It is not at all clear whether Rous's original strain was able to replicate on its own or if some descendants acquired this ability later. Very few acutely oncogenic or transforming retroviruses are capable of replication without a helper virus, making non-defective strains of RSV quite unique.