We have characterized the proximal promoter of the human alpha1(III) collagen gene (COL3A1). Transient transfection assays using a series of chimeric constructs linked to the luciferase gene indicated that the segment from -96 to -34 is necessary to activate transcription. Electrophoretic mobility shift assays (EMSAs) showed that the multiple proteins form the DNA-protein complex in different combinations depending on the cell types. A competition assay using mutant oligonucleotides showed that the sequence 5'-GCTCTCATATTTCAGAA-3' (-79 to -63 bp) is critical for DNA-protein complex formation. This sequence is contained in the B element of mouse alpha1(III) collagen gene (Col3a1) reported by Ruteshouse and de Crombrugghe (J. Biol. Chem., 1993). In the rhabdomyosarcoma cell line, A204, at least two proteins of 92-118 kDa and 40-52 kDa are involved in the DNA-protein complex bound to this motif.