The DNA sequence has been determined for a 3.8-kb region which encodes the mercury-resistance (mer) operon of the IncFII plasmid NRl. The sequence reveals 4 open reading frames which could encode proteins of 12,522, 9,429, 14,965, and 58,912 d corresponding to the 4 previously+described Hg-inducible proteins detected in minicells carrying mer plasmids. The Hg(II) reductase protein sequence is about 90% homologous to that of Tn501, but the DNA sequence shows a homology of 60–70% to that of Tn501 except for short regions of very high homology. The entire mer region is 63.4% G-C overall. The region encoding the merR (positive regulatory) function has 3 possible open reading frames, 2 of which overlap in one direction and the third of which reads in the opposite direction. Attempts to visualize the polypeptide(s) encoded by the merR cistron were unsuccessful.
KeywordsMercury Codon Cysteine Polypeptide Disulfide
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