The sequence and organization of the citrate synthase (TrCIT) and isocitrate lyase (TrICL) genes of Trichoderma reesei show that both genes are adjacent, transcribed in opposite directions, and share an intergenic region of a 646 bp. This region was found to be a TATA-less promoter rich in CpG islands, which seems to be a characteristic feature of bidirectional promoters in the human genome. Promoter deletion analysis showed that a 494-bp fragment (from -154 to –647 in relation to the ATG initiation codon of TrCIT) and a Sp1-binding site (located at -327) are necessary for transcription of both genes. A putative Sp1 transcription factor from T. reesei, showing 56.3 % and 53.7 % similarities to the human and mouse proteins, respectively, was cloned and used for electrophoretic mobility shifting assays. The results indicate that T. reesei Sp1 binds to the sequence GGGCGG and that this sequence is necessary for expression of TrCIT and TrICL.