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DNase I footprinting analysis of the proximal apoA-I promoter sequences with rat liver nuclear extracts identified four protected regions: A, -22 to +17; B, -128 to -77; C, -175 to -148; and D, -220 to -190. Region D (-220 to -190) binds at least two distinct activities, designated AID1 and AID2, respectively, which can be separated by ion exchange chromatography. Region C (-175 to -148) forms five DNA protein complexes. Three of the complexes (2, 4, and 5) originate from the binding of more than one heat-stable nuclear factor, and two (1 and 3), from the binding of two heat-labile factors. The heat-stable factors bind in the -175 to -148 region and can be distinguished from C/EBP, which recognizes the same region, with DNA binding gel electrophoretic assays. Both factors 1 and 3 bind in the -168 to -148 apoA-I region. Despite the lack of a CCAAT motif in this region, the binding of factor 1 is competed out by …