GENES ENCODING THERMOPHILIC ASPARTATE CARBAMOYLTRANSFERASES OF THERMUS-AQUATICUS ZO5 AND THERMOTOGA-MARITIMA MSB8 - MODES OF EXPRESSION IN ESCHERICHIA-COLI AND PROPERTIES OF THEIR PRODUCTS

Aspartate carbamoyltransferase genes from the extreme thermophilic eub acteria Ta. Maritima and T. aquaticus were cloned by complementation i n E. coli. Sequencing of the Ta. maritima pyrB gene, the aberrant beha viour of the enzyme product in E. coli, and comparison of the derived amino acid sequence with mesophilic ATCases suggest that the gene was disrupted in the process of cloning and that Thermotoga ATCase belongs to an unusual class of aspartate carbamoyltransferases. Analysis of t he proximal part of the T. aquaticus pyr operon and characterization o f the ATCase gene products formed in E. coli and in the original host led to the proposal that the T. aquaticus aspartate carbamoyltransfera se and dihydroorotase enzymes associate to form a stable multienzyme c omplex, regulated by UTP. Some indications of how the thermophilic ATC ase genes could be expressed in E. coli were also obtained.