Abstract: A stable, substantially nononcogenic vector having a cloning site for the convenient insertion of a gene of interest has been constructed by recombinant technology from an avian retrovirus. The construct is derived from Rous sarcoma virus and the cloning site is a replacement for the csr oncogene. This vector is useful for ferrying selected, expressible genes into avian germ cells for incorporation into the germ line. The vector is also useful for inserting and expressing foreign genes in somatic avian cells both in vivo and in vitro.

Abstract: A transgenic avian line, which is resistant to infection by avian leukosis virus (ALV), subgroup A, has been produced. The line was discovered as a chance event occurring in a program of infecting embryonic chickens with a recombinant ALV virus, selecting individuals assayed to be positive for genomic insertion of proviral sequences, and backcrossing to the original line to obtain G1 progeny demonstrating stable inheritance of the inserts. Of at least three proviral inserts defective for ALV production, one was found to be capable of expressing in the cell membrane subgroup A envelope glycoprotein which specifically interferes with infection by subgroup A virus. This insert represents an artificially introduced dominant gene for ALV disease resistance. Through an appropriate breeding program, a line of chickens homozygous for this gene has been obtained.