Mice with non-phosphorylated serine 389 in p53 are susceptible for bladder tumors induced by 2-acetylaminofluorene (2-AAF). Since p53 is a transcription factor, this might well be preceded by differences in the regulation of gene expression. Microarray analysis was used to determine early transcriptional changes that might underlie this cancer-prone phenotype. Interestingly, lack of Ser389 phosphorylation led to endogenously different gene expression levels. The number of genes affected was, however, rather small. Conversely, after short-term exposure to 2-AAF, wild-type and p53.S389A bladders demonstrated a significant number of differentially expressed genes. Differences between wild-type and p53.S389A could mainly be attributed to a delayed, rather than complete absence of, transcriptional response of a group of genes, including well-known p53 target genes involved in apoptosis and cell-cycle control like Bax, Perp and P21. An analysis of differentially expressed genes in non-tumorigenic tissue and bladder tumors of p53.S389A after long-term exposure to 2-AAF revealed 319 genes. Comparison of these with those found after short-term exposure resulted in 23 transcripts. These possible marker genes might be useful for the early prediction of bladder tumor development. In conclusion, our data indicate that lack of Ser389 phosphorylation results in aberrant expression of genes needed to execute vital responses to DNA damage. Post-translational modifications, like Ser389 phosphorylation, seem crucial for fine-tuning the transcription of a specific set of genes and do not appear to give rise to major changes in transcription patterns. As such, Ser389 phosphorylation is needed for some, but certainly not all, p53 functions.