Established in 1985 from a bursal lymphoma, which was induced by infection of a 1 day old chicken with Rous-associated virus type 1 (RAV-1), an avian leukosis retrovirus carrying no cell-derived oncogene; cells are described to retain the ability to rearrange the immunoglobulin light chain gene (IgL) and to exhibit a high frequency of homologous gene targeting