The structure of the mer operon.

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• The mercury-resistance (mer) operon confers resistance to toxic heavy metals in bacteria.
• Understanding the genetic basis of mercury resistance is crucial for environmental and clinical microbiology.
• The IncFII plasmid NR1 is a well-characterized plasmid system in bacterial genetics.

Purpose of the Study:

• To determine the complete DNA sequence of the mercury-resistance (mer) operon in the IncFII plasmid NR1.
• To identify the open reading frames (ORFs) encoding mercury-inducible proteins.
• To compare the DNA and protein sequences with other known mercury resistance determinants, such as Tn501.

Main Methods:

• DNA sequencing of a 3.8-kb region of the IncFII plasmid NR1.
• Bioinformatic analysis to identify open reading frames (ORFs).
• Sequence homology comparisons using established algorithms.

Main Results:

• The 3.8-kb region contains four ORFs encoding proteins of predicted molecular masses 12,522, 9,429, 14,965, and 58,912 Da.
• The Hg(II) reductase protein sequence exhibits approximately 90% homology to that of Tn501.
• The overall DNA sequence homology to Tn501 is 60-70%, with regions of higher homology observed.
• The merR regulatory region contains three potential ORFs, with complex overlapping arrangements.

Conclusions:

• The sequenced region represents the complete mercury-resistance (mer) operon of plasmid NR1.
• The high homology of the mer operon to Tn501 suggests a common evolutionary origin or horizontal gene transfer.
• Further investigation is needed to elucidate the function and expression of the merR regulatory region and its encoded polypeptides.