Scanning mutation analysis of 21PBA recognition sequence. (A) Juxtaposition of mutated sequences M1-M5 against the wild-type sequence. Successive 4-bp sequence elements are substituted with thymidine. Base changes affecting 21PBA binding are summarized at the bottom in bolded letters; sequences comprising a p53 consensus site are underlined. (B) Binding by mutant sequences is shown. Equal amounts of radiolabeled mutant (M1-M5) or wild-type (29) probe were incubated with HL-60 extract in gel-shift assay. Loss of binding to M4 and M5 and novel migration using the M3 target is evident. (C) The ability of mutant sequences to compete binding to the 29-bp target is shown. A 44-bp target labeled at low activity is shown in lane 1. HL-60 extract is incubated with radiolabeled 29-bp target after preincubation for 30 minutes with 30-fold excess of unlabeled 44-bp competitor and either 30- or 100-fold excess of unlabeled 29-bp or mutant competitor as shown.