Octamerization of lambda CI repressor is needed for effective repression of P(RM) and efficient switching from...

Area of Science:

• Molecular Biology
• Genetics
• Virology

Background:

• The CI repressor of bacteriophage lambda is a model system for studying cooperativity in genetic switches.
• CI dimers bind operator sites (O(R) and O(L)) to form tetramers, repressing lytic promoters and activating the cI gene.
• The physiological role of CI octamerization and its interaction with O(R)3 remains unclear.

Purpose of the Study:

• To investigate the mechanism of CI repressor function in bacteriophage lambda.
• To elucidate the role of distant operator binding in CI-mediated repression.
• To clarify the function of CI octamerization in maintaining lysogeny.

Main Methods:

• Genetic analysis of bacteriophage lambda mutants.
• Reporter assays to measure promoter activity.
• Electrophoretic mobility shift assays (EMSAs) to study protein-DNA interactions.

Main Results:

• Repression of the P(RM) promoter at lysogenic CI concentrations is dependent on the distant O(L) operator.
• A mutant defective in this negative autoregulation exhibits elevated CI levels and impaired switching from lysogeny to lytic development.
• Previous findings on Cro binding to O(R)3 are invalidated.

Conclusions:

• The octameric CI:O(R)-O(L) complex enhances CI affinity for O(R)3 by linking O(R)3 and O(L)3.
• This interaction is crucial for efficient CI negative autoregulation and maintaining lysogeny.
• The study provides new insights into the complex regulatory mechanisms of bacteriophage lambda.