Transcription of the beta-actin gene is rapidly inducible in response to serum stimulation. To determine the regions responsible for serum inducible and basal level expression, the human beta-actin promoter was subjected to mutational analysis. Two distinct elements, the CCAAT homology and the beta-actin specific conserved sequences, were found by a chloramphenicol acetyltransferase expression assay and sequence comparisons, and then analyzed for possible functions. Using a DNA bend assay, it was shown that the conserved sequences included the core of a sequence-directed bend of DNA. Gel mobility shift and DNase I protection assays revealed that the conserved sequences and the CCAAT homology were recognized by binding factors in HeLa cell extracts.