Structure of a Defective Provirus of Bovine Leukemia Virus

Defective proviruses of bovine leukemia virus (BLV) in the genomes of infected cells were investigated by using Southern blotting hybridization analysis with various portions of a cloned BLV DNA as probes. When nine independent tumors of enzootic bovine leukosis with a single proviral copy per cell were examined, a single defective provirus of BLV was found in one tumor and also in a bovine B cell line derived from this tumor. Hybridization analysis of this defective provirus revealed that it underwent deletion between the pol and env genes and contained no major deletion in the other regions.