A third gene affecting GABA transaminase levels inAspergillans nidulus

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Abstract
SUMMARY: Mutations in thegatB gene as well as mutations in the putative structural genegatA and the positive acting regulatory geneintA can affect γ-amino-n-butyrate (GABA) transaminase (EC 2.6.1.19) levels in the ascomycete fungusAspergillus nidulans. Partial or complete loss of function mutations ingatA,gatB andssuA, which specifies succinic semialdehyde dehydrogenase, can lead to accumulation of ω-amino acids resulting in pseudo-constitutivity and elevated expression of (retained) activities underintA control. These regulatory effects underlie selective methods forgatB−,ssuA−and leakygatA−mutations. However, all threegatB−alleles which have been selected lead only to partial loss of GABA transaminase activity as judged by bothin vivoandin vitrocriteria. It has not been established whether the leakiness of these threegatB−mutations is an allele-specific or a locus-specific effect and whether or not the GABA transaminase present ingatB−strains differs from the wild type enzyme. Thus the role of thegatB product remains to be elucidated. ThegatB gene is not closely linked to any other gene involved in ω-amino metabolism or related pathways.