Chromosome 1 contains the endogenous RAV-0 retrovirus sequences in chicken cells.

We have developed a structurally unique probe which can be used to determine the chromosomal location of nonreiterated genes in vertebrate organisms by the method of in situ hybridization. The probe consists of several specific RNA molecules attached by means of poly(A) . poly(BrdUrd) hybrids to 125I-labeled DNA of high molecular weight. The probe can be synthesized with a variety of RNA molecules, giving it versatility for detecting a variety of genes irrespective of gene size, copy frequency, and host genome complexity. Using this probe prepared with retrovirus genomic RNAs, we have physically mapped all three detectable endogenous genomes of Rous-associated virus type 0 (RAV-0) in Spafas gs- chf- (group-specific antigen negative, chicken helper factor negative) chicken fibroblasts to specific sites on chromosome 1. This finding suggests that these multiple nontranscribed RAV-0 genomes evolved through gene duplication of an original RAV-0 genome. The endogenous src gene coding for a 60,000-dalton protein also has been localized to one of the small macrochromosomes, 10, 11, or 12, in both chicken and Japanese quail cells. The results presented here are consistent with and greatly extend previously reported data obtained by using both chromosome fractionation and restriction endonuclease techniques and thus support the soundness of this hybridization approach.