BMC Genomics 2007, 8:139 http://www.biomedcentral.com/1471-2164/8/139 pF5ig3u-rreepr6essed target genes p53-repressed target genes. Panels A-D show site-specific qPCR ChIP results on left with standard deviation, where signifi- cance at p ≤ 0.05 is designated by an asterisk (*). Note the p53-occupied sequence in Panel B lies between genes which were both examined for changes in expression. Display and analyses are as described in Figure 4 legend. which different p53 binding locations have previously been described [5]. The majority of p53MH-predicted p53 binding sites within regions of validated occupancy contained either no spacer or a short spacer, in agreement with earlier data [5]. However, there are several notable exceptions to this trend including wnt7b, grhl3, shmt1 and sesn3 binding sites, which contain atypical spacers from 5–13 bp separating the individual half-sites, similar to the described p53- binding site within the siah promoter [55]. Consensus binding sites derived from our data are shown in Figure 9 using the WebLogo [56] sequence analysis tool. We report little deviation from the p53 consensus sequence for transactivation (Figure 9a) compared to repression except for the substitution of purine for pyrimidine at site 11 (Figure 9b). This data supports the capability for p53-reg- ulated transcriptional repression from a consensus bind- ing site [57]. Stimulus-dependent transcriptional regulation Experiments were conducted to determine if p53-regu- lated genes in differentiation were unique from those fol- lowing genotoxicity. Expression levels of NGF-dependent p53 target genes measured after DNA-damage by bleomy- cin and 5-fluorouracil were compared to NGF treatment to discriminate stimulus-dependency of p53-mediated transcription. As expected, expression levels for p21Waf1/ Cip1 and cyclin G1 were elevated following all treatments, confirming the transcriptional activity of p53 in all groups (Figure 10A). Increased expression levels in three of the NGF-responsive targets, wnt7b, pkcbpb15 and lect1 (Figure Page 8 of 17 (page number not for citation purposes)