Stable transcription factor complex formation and high-level clys gene expression are late events in macrophage differentiation. (A) In vivo DMS footprinting experiment analyzing transcription factor occupancy during in vitro differentiation (day 0 to day 9 and after LPS stimulation of day-9 cells) at clyscis-regulatory elements and the c-fms promoter as indicated. G indicates DMS-treated naked genomic DNA; ES, DNA prepared from lysozyme nonexpressing transgenic mouse ES cells. The nature and the position of transcription factor binding sites are indicated. Protection from methylation at G(N7) is indicated as a white circle, enhancement of DMS reactivity is indicated as a black circle, and weak enhancement is indicated as a gray circle. (B) Quantification of signals from selected bands (indicated by asterisks) of the gels depicted in panel A. The numbers represent the mean values and standard deviations of quantifications from 2 independent experiments and 2 separate gels, respectively.