An unusual arrangement of pur and lpx genes in the photosynthetic purple sulfur bacterium Allochromatium vinosum

The nucleotide sequence of a 1634 bp DNA fragment from the photosynthetic p urple sulfur bacterium Allochromatium vinosum contains one complete and two partial open reading frames. Sequence comparisons to genes from other orga nisms suggest that this A. vinosum DNA fragment contains, starting from the 5' end, the following: (1) 234 bp at the 3' end of the A. vinosum purH gen e, coding for 78 amino acids at the C-terminus of the bi-functional 5'-phos phoribosyl-5-aminoimidazole-4-carboxamide formyltransferase/IMP cyclohydrol ase (EC 2.1.2.3), an enzyme involved in de novo purine biosynthesis; (2) 77 7 bp of the A. vinosum lpxA gene, coding for all 259 amino acids of the UDP -N-acetylglucosamine-O-acyltransferase, an enzyme involved in lipid A biosy nthesis; and (3) 567 bp at the 5' end of the A. vinosum purD gene, coding f or 189 amino acids at the N-terminus of 5'-phosphoribosyl glycinamide synth etase (EC 6.3.4.13), a second enzyme involved in de novo purine biosynthesi s. The presence of a gene coding for an enzyme involved in lipid A biosynth esis between two genes coding for enzymes of the de novo purine biosynthesi s pathway represents a unique arrangement of these genes.