CHINESE-HAMSTER OVARY CELLS CONTAIN TRANSCRIPTIONALLY ACTIVE FULL-LENGTH TYPE-C PROVIRUSES

We have isolated a genomic locus from Chinese hamster ovary (CHO) cell s that contains a full-length provirus. Nucleotide sequence analysis i ndicates that it is a defective member of the rodent type C retrovirus family with an env region that is similar to those of mouse amphotrop ic retrovirus and subgroup B feline leukemia virus. We were able to de monstrate that this provirus is a member of a closely related family o f full-length proviruses in CHO cells and Chinese hamster liver. Hybri dization probes generated from this genomic clone were used to charact erize type C retrovirus RNA expression in CHO cells. Full-length genom ic RNA and subgenomic envelope mRNA were detected in CHO cell lines bu t not in the humnn-derived 293 cell line. Interestingly, we discovered that the site of retrovirus integration lies within a G repeat sequen ce belonging to the short interspersed element family of retroposons.