Mycobacterium sp. G3 was reported as a dibenzothiophene (DBT)-degrading microorganism and the first strain to have the ability to degrade high-molecular-weight alkyl DBTs, such as 4,6-di-butyl DBT and 4,6-dipentyl DBT, by the C-S bond cleavage pathway. Three genes (mdsA, mdsB, and mdsC) for desulfurization, which form a cluster, were cloned from Mycobacterium sp. G3. The expression of each gene in Escherichia coli JM109 showed that MdsC oxidized DBT to DBT sulfone, MdsA transformed DBT sulfone into 2-(2'-hydroxyphenyl)benzene sulfinate (HPBS), and MdsB desulfinated HPBS into 2-hydroxybiphenyl (HBP), indicating that the gene products of mdsABC are functional in the recombinant. MdsC oxidized 4,6-dimethyl DBT, 4,6-diethyl DBT, 4,6-dipropyl DBT and 4,6-dibutyl DBT to each sulfone form, suggesting that MdsC covers a broad specificity for alkyl DBTs.