138 

 Fig, 7-7. The latter shows two clusters, with Nta-AroD«E 

 grouping with the mono functional proteins of the 

 prokaryotes: E. coli, Salmonella typhimurium, Bacillus 

 subtilis, and Enterococcus faecalis. Thus, the 

 bifunctional plant enzyme is evolutionarily closer to the 

 prokaryote monofunctional proteins than to the AroD domains 

 of the pentafunctional proteins present in the eukaryotes, 

 yeast (Arol) and fungi (AroM) . 



The proteins in the multiple alignment shown in Fig. 7- 

 6 are separated between the two clusters that are shown in 

 Fig. 7-7 for clarity. This alignment shows the conserved 

 residues within each cluster, as well as those conserved 

 throughout both clusters. Three amino acids shown to be 

 important catalytic residues for the E. coli AroD protein, 

 HIS (25) , MET (47) , and LYS (20) are marked with asterisks, 

 and these are conserved in all proteins having AroD 

 catalytic activity. It has been suggested that the 

 repressor proteins from Neurospora crassa (Qa-lS) and from 

 Emericella nidulans (QutR) evolved from three of the five 

 domains of the pentafunctional protein corresponding to 

 dehydroquinase , shikimate dehydrogenase, and shikimate 

 kinase (38) . These retained the ability to bind what 

 previously were substrate molecules to function in a new 

 role as regulatory agents. Thus, critical residues such as 

 those marked by asterisks were altered to retain binding but 

 to lose catalysis. Note that nine other residue positions 



