A gene cluster encoding methylamine dehydrogenase (MADH) and its primary electron acceptor, azurin iso-2 (the initial step of Electron transport chains involved in methylamine oxidation) of the obligate methylotroph Methylomonas sp. strain J (Methylomonas J) was characterized. PCR products synthesized using primers based on the N- and C-terminal amino acid sequences of MADH light subunit from the facultative methylotroph Methylobacterium extorquens AM1 were used as probes for cloning. Fourteen open reading frames were found in a cloned EcoRI-PstI fragment consisting of a total of 11,549 bp. Eight open reading frames were identified as mauFBEDAGLM based on the high homology 19 those from Methylophilus methylotrophs W3A1-NS. The mauA acid mauB genes encode L subunit and H subunit of MADH, respectively. The mauO which encodes azurin iso-2, a primary electron acceptor from MADH of Methylomonas J. was located downstream from the mauFBEDAGLM genes and the direction of transcription of this gene was found to be opposite to that of the mau gene cluster. Northern blotting analysis suggested that the expression of the mau gene cluster and the mauO gene is co-regulated. These results suggest that dynamic gene recruitment occurred for the initial step of the electron transport chains involved in methylamine oxidation of methylotrophs.