cDNA Excision in Stable Retroviral cDNA Transfectants Is Prevented by R Removal

The present study provides evidence on the occurrence of DNA rearrangement between the redundant 5′ and 3′ R domains of equine infectious anemia virus (EIAV) Tat cDNA. This was correlated with a gradual loss of cDNA copy number concomitantly with a decrease in gene expression. Removal of the 5′ RU5 abolished rearrangement and stabilized Tat expression in EIAVtatcDNA transfectants. Our data suggest that prior removal of the 5′ R from cloned retroviral cDNAs can impede DNA rearrangement, thus preventing cDNA excision that frequently occurs and hinders permanent expression of retroviral cDNAs in stable transfectants.