Cro/C1-type helix-turn-helix domain (IPR001387)

Short name: Cro/C1-type_HTH

Overlapping homologous superfamilies

Domain relationships


The cro/C1-type HTH domain is a DNA-binding, helix-turn-helix (HTH) domain of about 50-60 residues present in transcriptional regulators. The domain is named after the transcriptional repressors cro and C1 of temperate bacteriophages 434 and lambda, respectively. Besides in bacteriophages, cro/C1-type regulators are present in prokaryotes and in eukaryotes. The helix-turn-helix DNA-binding motif is generally located in the N-terminal part of these transcriptional regulators. The C-terminal part may contain an oligomerization domain, e.g. C1 repressors and CopR act as dimers, while SinR is a tetramer. The cro/C1-type HTH domain also occurs in combination with the TPR repeat and the C-terminal part of C-5 cytosine-specific DNA methylases contains regions related to the enzymatic function.

Several structures of cro/C1-type transcriptional repressors have been resolved and their DNA-binding domain encompasses five alpha helices, of which the extremities are less conserved [PMID: 3187531]. The helix-turn-helix motif comprises the second and third helices, the third being called the recognition helix. The HTH is involved in DNA-binding into the major groove, where the recognition helix makes most DNA-contacts. The bacteriophage repressors regulate lysogeny/lytic growth by binding with differential affinity to the operators. These operators show 2-fold symmetry and the repressors bind as dimers. Binding of the repressor to the operator positions the DNA backbone into a slightly bent twist [PMID: 3187531, PMID: 11972345].

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0043565 sequence-specific DNA binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles