Disruption of a rhodaneselike gene results in cysteine auxotrophy in Saccharopolyspora erythraea.

A 3,373-base-pair DNA segment from a clone fortuitously isolated from Saccharopolyspora erythraea by hybridization to an oligodeoxynucleotide probe was sequenced. Computer-assisted analysis of the nucleotide sequence reveals three closely linked Streptomyces open reading frames plus a fourth converging on the others. The deduced product of one of them, ORF2, shows considerable similarity to bovine liver rhodanese. orf2, and the closely linked orf3 located just downstream of it, were disrupted by insertion of an apramycin resistance cassette into the orf2 coding sequence along with inversion of the fragment carrying most of orf2 and orf3 via two successive recombinational events in the wild-type strain. The mutant strain thus created contains wild-type levels of rhodanese activity but cannot grow on minimal medium. It is a cysteine auxotroph, capable of utilizing efficiently only thiosulfate among the inorganic sulfur sources tested. orf2 has been designated cysA. The possible role of the rhodaneselike cysA gene product in thiosulfate formation is discussed.