Two mini-F-encoded proteins are essential for equipartition.

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The mini-F plasmid's par region is vital for ensuring accurate partitioning of plasmid copies into daughter cells during cell division.
• This region, approximately 2.5 kb, encodes two essential proteins: F1 (41 kDa) and F2 (37 kDa).

Purpose of the Study:

• To investigate the roles of the F1 and F2 proteins in the plasmid equipartition process mediated by the par region.
• To identify and characterize mutants affecting plasmid stability and segregation.

Main Methods:

• Isolation and characterization of 13 mutants of a phage lambda-mini-F hybrid exhibiting unstable plasmid formation.
• Identification of two fully suppressible nonsense (amber) mutants within the par region.

Main Results:

• The amber mutant par-41 specifically inhibited F1 synthesis, producing a large nonsense fragment.
• The amber mutant par-36 specifically abolished F2 synthesis.
• Both F1 and F2 proteins were found to be indispensable for proper plasmid equipartition.

Conclusions:

• The par region's ability to promote plasmid equipartition is dependent on the functional integrity of both F1 and F2 proteins.
• These findings highlight the critical roles of F1 and F2 in the molecular mechanisms of plasmid segregation.