Lambda cI repressor mutants altered in transcriptional activation

Area of Science:

• Molecular Biology
• Genetics
• Bacteriophage Lambda Research

Background:

• The lambda cI repressor regulates gene expression in bacteriophage lambda.
• Positive control (pc) is crucial for efficient gene activation by the cI repressor.
• Understanding pc mechanisms requires analyzing repressor mutants with altered functions.

Purpose of the Study:

• To analyze the in vivo functions of three lambda cI repressor mutants defective in positive control.
• To investigate the impact of specific amino acid substitutions on repressor DNA binding and activation.
• To elucidate the role of residues at positions 34, 38, and 43 in cI repressor activity.

Main Methods:

• Constructed a lambda cI repressor expression system for controlled in vivo expression.
• Measured PRM promoter activation by wild-type and mutant cI repressors.
• Studied DNA binding properties of repressors and mutants using various operator constructs in vivo.

Main Results:

• Wild-type cI repressor showed a five-fold activation of the PRM promoter.
• Two mutants (G43-R, E34-K) repressed the PRM promoter, indicating altered DNA binding.
• One mutant (D38-N) retained DNA binding but lost activation function, behaving as a true pc mutant.
• Amino acid substitutions at position 38 (D38-N, D38-Y, D38-F) differentially affected activation and binding.

Conclusions:

• Amino acid changes at positions 34 and 43 primarily impact lambda cI repressor binding properties.
• Hydrophobic residues at position 38 are as functional, or more so, than the wild-type acidic residue for activation.
• The D38-N mutant provides a model for studying positive control mechanisms independently of DNA binding.