CYP153 a cytochrome P450 from Acinetobacter sp. EB104 catalyzes the hydroxylation of unsubstituted n-alkanes. We have decided to use the CYP153 system as a model for mechanistic studies on regioselective n-alkane oxidation and the interaction of hydrophobic substrates with soluble enzymes. Here the molecular cloning of the CYP153 gene is reported. Single specific primer PCR was applied to yield the whole gene sequence via chromosomal walks. CYP153 consists of 497 amino acids (M-r = 56 kDa) and thus represents an unusually long bacterial P450, containing all P450 typical structural elements. It constitutes the new P450 family CYP153. The prolonged N-terminus of about 90 amino acids does not contain a so far known membrane-anchoring sequence but a 28-amino acid long amphipathic helix. The relevance of the remarkably long N-terminus and of other sequence motives like the hydrophobic F-G loop is discussed with respect to substrate binding and recognition.