Molecular Aspects of ara Regulation

THE ara REGULON In Escherichia coli , the metabolism of L-arabinose involves the expression of six genes, araA through araF (Englesberg 1971; Englesberg and Wilcox 1974). These genes are located at three different regions on the E. coli chromosome (Fig. 1). Genes araA , araB , araC , and araD are located between the threonine and leucine operons, at approximately 1 minute (min) on the circular linkage map of E. coli (Gross and Englesberg 1959; Englesberg 1961; Englesberg et al. 1962; Bachman et al. 1976). The araE gene is located at about 61 min between thyA and serA (Novotny and Englesberg 1966), and the araF gene has been tentatively mapped at 44–45 min, close to the structural genes for the histidine operon and the galactose binding protein (R. Hogg, pers. comm.). Genes araB , araA , and araD , together with their controlling sites araI and araO , constitute a single unit of transcription, the araBAD operon (Englesberg 1971; Englesberg and Wilcox 1974; Schleif and Lis 1975). The structural genes code for L-ribulokinase ( araB ) (Lee and Englesberg 1962; Lee and Bendet 1967; Lee and Patrick 1970), L-arabinose isomerase ( araA ) (Lee and Englesberg 1962; Patrick and Lee 1968, 1969), and L-ribulose 5-phosphate 4-epimerase ( araD ) (Lee et al. 1968), the first three enzymes of L-arabinose catabolism (Fig. 1). Genes araE and araF are both involved in active transport of L-arabinose (Novotny and Englesberg 1966; Hogg and Englesberg 1969; Schleif 1969). The araE gene may code for a membrane protein (R. Hogg, pers. comm.), whereas the araF gene codes for...