FIG. 1.

Experimental design for MMTV proviruses with CDP binding site mutations. (A) Scheme for analysis of CDP binding site mutants. The 5′ half of the hybrid infectious provirus is composed of the 5′ LTR and gag-pol genes from the endogenous Mtv-1 provirus, whereas the 3′ end is composed of the env and 3′ LTR from a C3H MMTV provirus. An inverted triangle represents the CDP binding site mutations within the U3 region of the LTR. Transfection of proviral DNA leads to integration and transcription from the 5′ LTR by RNA polymerase II followed by RNA packaging into virions. Subsequent infection will allow RT of viral RNA so that the 3′ LTR mutations are duplicated in the 5′ LTR of the provirus. BALB/c mice were injected with XC cells containing the stably transfected proviruses and analyzed for T-cell deletion and the appearance of tumors. (B) Positions of mutations introduced in the distal NRE (dNRE) and proximal NRE (pNRE) of MMTV proviruses.