FIG. 6.

Localization of the functional B-cell enhancer region within the MMTV pol gene. (A) Enhancer activity of MMTV pol gene regions. (B) Nucleotide sequence of the MMTV pol gene enhancer region. The MMTV pol region (nt 5055 to 6255) in pGL2-pol 3+ was successively truncated from the 5′ terminus (solid arrowhead) and from the 3′ terminus (open arrowhead). The truncation mutants were transfected into LBB.11 B cells. After 24 h, the cells were harvested and lysed and the luciferase activity and protein concentrations determined. The numbers indicate the position of the test fragment within the MMTV provirus. Specific truncation mutants are identified below the graph for the 5′ truncation series (solid circles) and above the graph for the 3′ truncations (open circles). The truncation mutant 6252 represents the vector control and is identical to the plasmid pGL2-Promoter (Promega). The bars below the graph represent the pol gene fragment analyzed, with the shaded portions indicating the parts required for enhancer activity in the respective 5′ and 3′ truncations and the hatched portions specifying the dispensable parts. Approximate positions of the env gene and splice acceptor (SA) site are indicated.