A novel benzene monooxygenase gene cluster has been cloned from Pseudomonas aeruginosa J104 which was isolated from soil as a benzene degrader. The nucleotide sequence of this gene cluster was found to be highly homologous to those of other toluene monooxygenase gene clusters. This multicomponent monooxygenase also has the capability to catalyze the hydroxylation of various alkylated aromatic hydrocarbons. The low regiospecific hydroxylation was observed when toluene, o-xylene, ethyl benzene and n-propyl benzene were used as substrates.