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The genes encoding the catalytic (pyrB) and regulatory (pyr!) polypeptides of aspartate transcarbamoylase (ATCase, EC 2.1.3.2) from several members of the family Enterobacteriaceae appear to be organized as bicistronic operons. The pyrBI gene regions from several enteric sources were cloned into selected plasmid vectors and expressed in Escherichia coli. Subsequently, the catalytic cistrons were subcloned and expressed independently from the regulatory cistrons from several of these sources. The regulatory cistron of E. coli was cloned separately and expressed from lac promoter-operator vectors. By utilizing plasmids from different incompatibility groups, it was possible to express catalytic and regulatory cistrons from different bacterial sources in the same cell. In all cases examined, the regulatory and catalytic polypeptides spontaneously assembled to form stable functional hybrid holoenzymes. This hybrid enzyme formation indicates that the r:c domains of interaction, as well as the dodecameric architecture, are conserved within the Enterobacteriaceae. The catalytic subunits of the hybrid ATCases originated from native enzymes possessing varied responses to allosteric effectors (CTP inhibition, CTP activation, or very slight responses; and ATP activation or no ATP response). However, each of the hybrid ATCases formed with regulatory subunits from E. coli demonstrated ATP activation and CTP inhibition, which suggests that the allosteric control characteristics are determined by the regulatory subunits.

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state. When the state systems were dismantled, hundreds of people at these research facilities and field stations lost their jobs. Most institutes immediately downsized by half and have since been forced to make further reductions. Though some lost jobs were superfluous or redundant, the collapse of these communities has affected the scale of scientific endeavor and the morale of the scientists who remained. To generate revenues, many research institutes have become quite creative. It is now common to find institutes contracting out services for soil testing, seed production, plant breeding, vaccine development, artificial insemination, water analysis, etc. Some of these contracts are held with local farmers, while others are held with government ministries and the emerging private sector. International companies frequently contract with research facilities to support market development or related research and development. Entrepreneurial scientists from the region are exploring every avenue to keep their research interests alive. For this purpose, they are looking to the agricultural research community in Europe and the United States for collaboration. This need provides a rare opportunity for the U.S. researchers to tap the energies of a well-trained pool of scientists for common benefit.