NUCLEOTIDE-SEQUENCE OF THE MXCQ AND MXCE GENES, REQUIRED FOR METHANALDEHYDROGENASE SYNTHESIS IN METHYLOBACTERIUM-ORGANOPHILUM-XX - A 2-COMPONENT REGULATORY SYSTEM

Nucleotide sequence analysis of the mxcQ and mxcE loci, required for t he synthesis of methanol dehydrogenase in Methylobacterium organophilu m XX, has revealed two open reading frames that show significant simil arity to sequences of prokaryotic two-component systems, especially Mx aY and MxaX proteins of another methylotrophic bacterium, Paracoccus d enitrificans. Cell-free extracts and DNA-column-fractionated proteins from wild-type M. organophilum XX cells grown on methanol or succinate contained protein(s) that were able to bind specifically to the upstr eam region of methanol dehydrogenase large subunit gene (mxaF). In con trast, cell-free extracts from mxcQ and mxcE mutant strains of M. orga nophilum XX had zero or reduced binding activity towards the promoter fragments of the mxaF gene. This is consistent with the involvement of the mxcQ and mxcE genes in transcriptional regulation of methanol deh ydrogenase synthesis. Analyses of sequential deletions of the mxaF ups tream region have defined the functional boundary of the promoter/oper ator region of this gene and identified one nucleotide segment as esse ntial to the activation of mxaF.