cII binds DNA as a tetramer, composed of identical 11 kDa subunits.
Although the cII gene encodes 97 codons, the mature cII protein subunit only contains 95 amino acids due to post-translational cleavage of the first two amino acids (fMet and Val).
cII is toxic to bacteria when overexpressed, as it inhibits DNA synthesis.

cII binds to a homologous region 35 base pairs upstream of the promoters pI, pRE and pAQ.
Unlike other DNA binding proteins, cII recognizes a direct repeat sequence TTGCN₆TTGC rather than sequences that form palindromes.
cII binds DNA ~2 orders of magnitude less strongly than the lambda repressor cI (3), and has a dissociation constant of ~80nM. DNA binding is achieved using the common helix-turn-helix motif (15), located between residues 26 and 45.
On either side of the DNA-binding domain are domains crucial for tetramer formation, located in residues 9-25 and 46-71.
cII's inherent in vivo instability stems from a C-terminal degradation tag, consisting of residues 89-97.
This tag is recognized by host proteases HflA and HflB, cause rapid proteolysis cII.
Although the C-terminal tag is still accessible when cII is tetramerized  (13), the rate of proteolytic degradation decreases, since Hfl proteases only degrade cII monomers.
cII binds DNA as a tetramer, composed of identical 11 kDa subunits. Although the cII gene encodes 97 codons, the mature cII protein subunit only contains 95 amino acids due to post-translational cleavage of the first two amino acids (fMet and Val). cII is toxic to bacteria when overexpressed, as it inhibits DNA synthesis.
cII binds to a homologous region 35 base pairs upstream of the promoters pI, pRE and pAQ. Unlike other DNA binding proteins, cII recognizes a direct repeat sequence TTGCN₆TTGC rather than sequences that form palindromes. cII binds DNA ~2 orders of magnitude less strongly than the lambda repressor cI (3), and has a dissociation constant of ~80nM. DNA binding is achieved using the common helix-turn-helix motif (15), located between residues 26 and 45. On either side of the DNA-binding domain are domains crucial for tetramer formation, located in residues 9-25 and 46-71. cII's inherent in vivo instability stems from a C-terminal degradation tag, consisting of residues 89-97. This tag is recognized by host proteases HflA and HflB, cause rapid proteolysis cII. Although the C-terminal tag is still accessible when cII is tetramerized  (13), the rate of proteolytic degradation decreases, since Hfl proteases only degrade cII monomers.
CII protein