Summary: After EMS mutagenesis, mutants of DSM 760 unable to synthesize pyrroloquinoline quinone (PQQ) were selected among mutants which did not utilize methanol but were still able to use methylamine as growth substrate. Six different genes () were identified by complementation analysis. The , cloned in a single R' plasmid, were grouped in a 3·9 kb DN A fragment. The genes and belonged to a single transcription unit independent from the adjacent gene The gene was contained in a short DNA segment of approximately 01 kb, separated from by a region with no apparent role in PQQ biosynthesis. Two other genes were identified: , which was closely linked to ; and , located approximately 19 kb from the other genes. Directed mutagenesis by marker exchange provided chromosomal insertion mutations of these genes in Attempts to express the genes in two heterologous hosts, and , were unsuccessful, and no plasmid containing all of the genes was isolated.


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