['Cellular transcriptional regulatory factor YY1 represses the activity of the early promoter P97 of HPV 16, but the regulatory activity to early promoter P105 of HPV 18 depends on a switch region which locates at the upstream sequences of YY1 binding sites. This study is to find out whether within the HPV 16 LCR there is such motif.', 'DNA sequences of the whole HPV 16 LCR region were analyzed. Two similar switch structures were found. Different CAT reporter plasmids, one containing HPV 16 reference and the other mutated LCRs, both starting at the end of L1 and from the beginning of the enhancer, were generated and transfected in HeLa cells transiently.', 'CAT assays showed there is no change of regulation pattern of YY1 on P97, when the two switch-similar structures were deleted. Sequences analysis also showed that no switch region like motif could be demonstrated in enhancer region, in promoter proximal segment, and even in E6/E7 area.'] Is [ No switch region found in the regulatory sequence of HPV 16 for promoter P97 ]?