Genes for the human mitochondrial trifunctional protein alpha- and beta-subunits are divergently transcribed from a common promoter region

Human HADHA and HADHB genes encode the subunits of an enzyme complex, the t rifunctional protein, involved in mitochondrial beta-oxidation of fatty aci ds. Both genes are located in the same region of chromosome 2p23. We isolat ed genomic clones, including 5' flanking regions, for HADHA and HADHB. Sequ encing revealed that both of these genes are linked in a head-to-head arran gement on opposite strands and have in common a 350-bp 5' flanking region. The 5' flanking region has bidirectional promoter activity within this regi on; two cis elements proved critical for the activity. Transcription factor Sp1 functions as an activator for the bidirectional promoter by binding to both elements. Therefore, expression of trifunctional protein subunits are probably coordinately regulated by a common promoter and by Sp1.