Organization of genes for tetrapyrrole biosynthesis in Gram-positive bacteria

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Abstract
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 uroporphrinogen III (Urolll) from glutamyl-tRNA. In P. macerans, the hem genes for Urolll synthesis are also closely linked but their organization is different: there is no hemX gene and the gene cluster also contains genes, cysGB and cysGA-hemD, encoding the enzymes required for synthesis of sirohaem from Urolll. 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 Urolll. 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 Uroll and NasF seems to be specific for nitrite reduction.

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