The Aspartate transcarbamoylases (ATCases) of divergent organisms, and in particular of enterobacteria, are sufficiently similar to organize in comparable tertiary domains and to assemble in similar quaternary aggregates. Nevertheless, they differ from each other by their catalytic properties and allosteric responses. Various intergenic fusions have been carried out from bacterial cistrons and hamster cDNA clones and their characterization is underway. The sequences of catalytic and regulatory chains have been determined. These will be compared in the hope that a sufficient number of sequence: function comparisons will permit deduction of critical structure/function relationships. Site specific mutagenesis will be performed aimed at elucidating the function of each segment of these catalytic and regulatory polypeptides. Monoclonal antibodies will be used to compare surface structures of the enzyme from different species. Collaboration with x-ray crystallographers should provide definitive structural information of interesting mutationally altered proteins. This is an excellent model system for such studies and Dr. Wild's past work makes him uniquely qualified for what is proposed.
