A whole genome view of prokaryotic haem biosynthesis.

Haem is the prosthetic group of proteins involved in many processes, and is also a regulatory molecule that mediates cellular responses to oxygen, iron and haem itself. Haem is synthesized in a multistep biosynthetic pathway with well-defined intermediates. Accordingly, the enzymes of the pathway are, to a large extent, conserved among prokaryotes and eukaryotes. Although individual haem biosynthesis genes and enzymes have been studied in many prokaryotic systems, only in few organisms has the entire pathway been examined. The availability of whole genome sequences allows an initial snapshot of the entire pathway at the genetic level in many diverse organisms. Unlike model systems, the genome represents a starting point for the detailed characterization of some unusual prokaryotes, and therefore examining haem synthesis genes can give important insight into core metabolism on which to lay the foundation for future experiments.