Activity of β-gal reporter constructs in a stably transfected hematopoietic cell line (FDC-P1) and NIH3T3 fibroblasts.vav DNA fragments encompassing the indicated HS sites (arrowheads) were linked to the β-gal gene (lacZ) and a β-globin intron and polyadenylation signal (see the Materials and Methods). The unfilled box denotes vav 5′ untranslated sequences. Where included, the HS5 intronic site was placed 3′ of the reporter polyadenylation site. The β-gal activity in extracts from three to five independent pools of FDC-P1 transfectants and two to three pools of NIH3T3 transfectants (3 independent determinations per pool) was related to that of a pool transfected with a construct containing the SRα promoter (assigned 100% activity). Means (±SEM) of the results are shown.