ORGANIZATION OF METHYLAMINE UTILIZATION GENES (MAU) IN METHYLOBACILLUS-FLAGELLATUM KT AND ANALYSIS OF MAU MUTANTS

The organization of genes involved in utilization of methylamine (mau genes) was studied in the obligate methylotroph 'Methylobacillus flage llatum' KT. Nine open reading frames were identified as corresponding to the genes mauFBEDAGLMN. In addition, an open reading frame (orf-l) encoding a polypeptide with unknown function was identified upstream o f the mau gene cluster. Subclones of the 'M. flagellatum' KT gene clus ter were used for complementation of a series of chemically induced ma u mutants of 'M, flagellatum' KT. Mutants in mauF, mauB, mauE/D, mauA, mauG, maul and mauM were identified. Two mutants (mau-18 and mau-19) were not complemented by the known mau genes, Since none of the chemic ally induced mutants studied had a defect in orf-l or mauN, insertion mutants in these genes were constructed. Phenotypically the mutants fe ll into three groups. The mauF, mauB, mauE/D, mauA, mauG, maul and mau M mutants do not grow on methylamine as a source of carbon and lack me thylamine dehydrogenase activity, but they synthesize both the large a nd the small subunit polypeptides albeit at different ratios, The mau- 18 and mau-19 mutants do not grow on methylamine as a source of carbon , and lack both methylamine dehydrogenase activity and the methylamine dehydrogenase subunits, The orf-l and mauN mutants grow on methylamin e as a source of carbon and synthesize wild-type levels of methylamine dehydrogenase. It has been shown earlier that the product of the mauM gene is not required for synthesis of active methylamine dehydrogenas e in Methylobacterium extorquens AM1 and Paracoccus denifrificans. How ever, MauM is required for synthesis of functional methylamine dehydro genase in 'M. flagellatum'.