When stably expressed at a low level in U2OS cells, HPV16
E2 upregulates SF2/ASF expression (41). A three- to fourfold
level of upregulation was observed consistently in three individual
E2-expressing cell clones (A4, B1, and B3). In order to
test if HPV16 E2 could transactivate, the SF2/ASF promoter,
a region from nt 1024 to 25 with respect to the transcriptional
start site, was PCR amplified from HeLa cell genomic DNA
and inserted upstream of the CAT gene in pGCAT3B to give
pGCAT3-B-SF2pr. This region should cover the transcription
initiation site and the proximal and distal promoter regions.