Functional analysis of the yeast plasmid partition locus STB

Area of Science:

• Molecular Biology
• Yeast Genetics
• Plasmid Biology

Background:

• Yeast 2-micron plasmid stability is crucial for genetic applications.
• The cis-acting locus STB (REP3) is known to be involved in plasmid maintenance.
• Conflicting reports exist regarding STB's precise function in partitioning and copy number control.

Purpose of the Study:

• To resolve controversies surrounding the STB locus function in yeast 2-micron plasmids.
• To elucidate the specific roles of STB in plasmid partitioning and copy number regulation.
• To characterize the functional domains within the STB locus.

Main Methods:

• Construction of yeast 2-micron plasmid derivatives with conditional STB function.
• Analysis of plasmid distribution and copy number in yeast populations.
• Functional dissection of the STB locus into proximal and distal domains.
• Assessment of transcriptional interference on STB function.

Main Results:

• Inactivation of STB leads to plasmid concentration in a subset of cells, not altered copy number.
• STB comprises two domains: STB-proximal (for partitioning) and STB-distal (for protection and transcription repression).
• STB-proximal function is sensitive to transcription, while STB-distal can be replaced by a terminator fragment.

Conclusions:

• STB is essential for proper plasmid partitioning in yeast, not copy number control.
• STB-distal protects STB-proximal from transcriptional interference and contains a transcription repressor element.
• Understanding STB function clarifies yeast plasmid instability and replication inhibition phenomena.