CLONING AND OVEREXPRESSION OF THE RHODOBACTER-CAPSULATUS HEMH GENE

In photosynthetically grown Rhodobacter capsulatus; heme is a qualitat ively minor end product of the common tetrapyrrole pathway, but it may play a significant regulatory role, Heme is synthesized from protopor phyrin by the product of the hemH gene, ferrochelatase. We have cloned the R. capsulatus hemH gene by complementation of an Escherichia coli hemH mutant, When a plasmid carrying the hemH gene is returned to R, capsulatus, ferrochelatase activity increases, aminolevulinate synthas e activity decreases, and bacteriochlorophyll levels are dramatically lowered. This is the first in vivo evidence to suggest that heme feedb ack inhibits aminolevulinate synthase in R. capsulatus, thereby reduci ng porphyrin synthesis.