Organisation of genes for tetrapyrrole biosynthesis in Gram-positive bacteria

Clusters of genes encoding enzymes for tetrapyrrole biosynthesis were cloned from Bacillus sphaericus, Bacillus stearothermophilus, Brevibacillus brevis and Paenibacillus macerans. The sequences of all hemX genes found, and of a 6.3 kbp hem gene cluster from P. macerans, were determined. The structure of the hem gene clusters was compared to that of other Gram-positive bacteria. The Bacillus and Brevibacillus species have a conserved organization of the genes hemAXCDBL, required for biosynthesis of uroporphyrinogen III (UroIII) from glutamyl-tRNA. In P. macerans, the hem genes for UroIII synthesis are also closely linked but their organization is different: there is no hemX gene and the gene cluster also contains genes, cysC(B) and cysG(A)-hemD, encoding the enzymes required for synthesis of sirohaem from UroIII. Bacillus subtilis contains genes for three proteins, NasF, YlnD and YlnF, with sequence similarity to Escherichia coli CysG, which is a multi-functional protein catalysing sirohaem synthesis from UroIII. It is shown that YlnF is required for sirohaem synthesis and probably catalyses the precorrin-2 to sirohaem conversion. YlnD probably catalyses precorrin-2 synthesis from UroIII and NasF seems to be specific for nitrite reduction.