EVIDENCE FOR A NOVEL CLASS OF MICROBIAL 3-DEOXY-D-ARABINO-HEPTULOSONATE-7-PHOSPHATE SYNTHASE IN STREPTOMYCES-COELICOLOR A3(2), STREPTOMYCES-RIMOSUS AND NEUROSPORA-CRASSA

The tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate ( DAHP) synthases from Streptomyces coelicolor A3(2), Streptomyces rimos us and Neurospora crassa have been purified to homogeneity. All three enzymes have a subunit M(r) of 54000. The S. coelicolor DAHP synthase was physically and kinetically characterized and the N-terminal amino acid sequence was obtained. The N-terminal amino acid sequence could n ot be obtained for the enzymes from S. rimosus and N. crassa, their N- termini apparently being blocked. However, following proteolytic diges tion, internal amino acid sequences were obtained from both enzymes. A comparison with the known DAHP synthase sequences indicated that thes e DAHP synthases are unrelated to other microbial DAHP synthase sequen ces but are similar to plant DAHP synthases. Up until now, two distinc t classes of DAHP synthase have been described, one comprising exclusi vely enzymes from plants, the other restricted to enzymes from micro-o rganisms. These studies indicate that the class containing the plant D AHP synthases also contains enzymes from a microbial eukaryote and fro m several bacteria.