The minimal sequence needed to define a functional DNA terminator in Bacillus subtilis

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Bacillus subtilis utilizes a 47 bp DNA replication terminator (IRI) essential for regulating DNA replication termination.
• The IRI terminator contains two binding sites, A and B, for the replication terminator protein (RTP), with each site accommodating an RTP dimer.

Purpose of the Study:

• To investigate the functional significance of specific base pairs within the Bacillus subtilis IRI DNA replication terminator.
• To elucidate the relationship between replication terminator protein (RTP) binding affinity and in vivo terminator function.

Main Methods:

• Systematic deletion mutagenesis of the IRI terminator sequence.
• In vivo assessment of DNA replication fork arrest activity.
• Electrophoretic mobility shift assays (EMSAs) to evaluate RTP binding affinity to truncated IRI sequences.

Main Results:

• Deletion of base pairs 1-2 from IRI abolished in vivo terminator function and RTP binding to site A.
• Deletions at the proximal end (base pairs 34-47) reduced function by ~50% with largely unaffected RTP binding.
• Further deletions into the RTP contact region impaired both in vivo function and RTP binding, with a truncated sequence (bp 1-24) showing minimal activity and altered B site binding.

Conclusions:

• Specific RTP-DNA contacts within the IRI terminator, particularly involving sites A and B, are critical for efficient DNA replication termination.
• While RTP binding is necessary, the overall binding affinity alone may not solely determine the efficacy of DNA replication termination.