Figure 9. Model describing the role of p68 at the PLK1 promoter. The PLK1 promoter/gene is shown as a schematic and is not to scale. (1) p53 binds to 2 previously established p53-responsive elements: p53RE-1 and p53RE-2, respectively, both under normal un-stimulated conditions and following induction of p53 by DNA damage stimuli or the MDM2 inhibitor, Nutlin-3.42 (2) Based on the data in Figures 4 and 8, p68 is likely to be recruited to a site(s) located approximately between −742 and +24, independently of the presence of p53. (3) The data also suggest that p53 occupancy of p53RE-2 occludes, either directly or indirectly, the recruitment of p68 to this region. (4) In the presence of wild-type p53, p68 recruitment may actually assist repression of PLK1 expression by p53.