Cloning and DNA sequence analysis of the mercury resistance genes of Streptomyces lividans.
1992
Sedlmeier R. | Altenbuchner J.
A broad-spectrum mercury resistance locus (mer) from a spontaneous chloramphenicol-sensitive (CmS), arginine auxotrophic (Arg) mutant of Streptomyces lividans 1326 was isolated on a 6 kb DNA fragment by shotgun cloning into thr mercury-sensitive derivative S. lividans TK64 using the vector pIJ702. The mer genes form part of a very large amplifiable DNA sequence present in S. lividans 1326. This element was amplified to about 20 copies per chromosome in the CmS Arg- mutant and was missing from strains like S. lividans TK64, cured for the plasmid SLP3. DNA sequence analysis of a 5 kb region encompassing the whole region required for broad-spectrum mercury resistance revealed six open reading frames (ORFs) transcribed in opposite directions from a common intercistronic region. The protein sequences predicted from the two ORFs transcribed in one direction showed a high degree of similarity to mercuric reductase and organomercurial lyase from other gram-negative and gram-positive sources. Few, if any, similarities were found between the predicted polypeptide sequences of the other four ORFs and other known proteins.
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