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J. Bacteriol., 05 1995, 2760-2768, Vol 177, No. 10
Copyright © 1995, American Society for Microbiology

Regulation of 5-aminolevulinic acid synthesis in Rhodobacter sphaeroides 2.4.1: the genetic basis of mutant H-5 auxotrophy

JH Zeilstra-Ryalls and S Kaplan
Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston 77225, USA.

Rhodobacter sphaeroides H-5 was isolated as a 5-aminolevulinic acid (ALA) auxotroph following treatment of wild-type cells with N-methyl-N- nitroso-N'-nitroguanidine (J. Lascelles and T. Altshuler, J. Bacteriol. 98:721-727, 1969). The existence in R. sphaeroides 2.4.1 of the genes hemA and hemT, each encoding the enzyme 5-aminolevulinic acid synthase (EC 2.3.1.37), raised questions as to the genetic basis for the ALA auxotrophy in mutant H-5. We therefore cloned both the hemA and hemT genes from mutant H-5. The hemA gene has been sequenced in its entirety and bears four base pair substitutions which encode three amino acid changes relative to the sequence of wild-type strain 2.4.1. Complementation analysis of an Escherichia coli ALA auxotroph has revealed that the loss of ALA synthase activity in the HemA mutant enzyme could be localized to two of the amino acid substitutions. On the other hand, the hemT gene from mutant H-5 was able to complement an E. coli mutant requiring ALA for growth. Complementation analyses were also carried out by introducing the cloned hemA or hemT gene of mutant H-5 or wild-type 2.4.1 in trans into H-5 and, in parallel, into our previously described HemA-HemT double mutant strain AT1 (E. L. Neidle and S. Kaplan, J. Bacteriol. 175:2304-2313, 1993). This analysis revealed that while the complementation pattern of mutant AT1 parallels that for the E. coli ALA auxotroph, mutant H-5 could only be complemented by the wild-type hemA gene. (ABSTRACT TRUNCATED AT 250 WORDS)


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