Isolation of Haemin-requiring Mutants of Escherichia coli K12

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Abstract
Hemin-requiring mutants (55) were isolated from hemin-premeable mutants. According to their growth responses to heme precursors and their patterns of porphyrin accumulation, the 55 mutants fell into 3 groups which were judged to have defects in 5-aminolevulinate dehydratase, ferrochelatase and uroporphyrinogen III cosynthase or uroporphyrinogen decarboxylase. In mutants of the group deficient in 5-aminolevulinate dehydratase, the mutations were adjacent to lac, and evidence is presented that the mutations were in hemB and were commonly deletions extending into proC.