Genetic Manipulation of Aspartate Transcarbamylases from Escherichia coli and Serratia Marcescens

Abstract

Aspartate transcarbamylase (ATCase, EC 2.1.3.2) allosterically modulates de novo pyrimidine biosynthesis in the enteric bacteria. This modulation differs in Escherichia coli and Serratia marcescens, with CTP allosterically inhibiting ATCase from E. coli and activating the enzyme in S. marcescens. The enzyme is composed of two catalytic trimers and three regulatory dimmers encoded by the pyrB and pyrI genes respectively. These adjacent cistrons are organized into a single control region to achieve coordinated biosynthesis of the catalytic and regulatory polypeptide chains necessary to form the holoenzyme. The genes for ATCase from the two organisms may be manipulated by in vitro recombinant DNA techniques. After the structure of the pyrBI genes encoding ATCase are characterized, they may be genetically altered and then transformed back into appropriate strains. The in vivo effects may then be studied. Eventually, DNA sequencing may be done for evaluation of evolutionary trends.