Learning about the structure of the CRO Repressorprotein

Khabil Miah CRO Repressor Protein

Learning about the structure of the CRO Repressor protein

As we all know; a proteins structure can be found in the cell wall in a bacteria or a membrane of eukayrotic, extracellular matrise. They function as enzymes or catalysts to either speed up or slow down a chemical reaction. These proteins produce antibodies within the cell immune system for protection against harmful cells. Other functions include the transport and storage of protein molecules and also control the growth and differentiation.

Cro and Repressor are part of the lysogenic/lytic growth switch mechanism in bacteriophage and function through transcription regulation at operons.

DNA binding is conducted as a homodimer. Each monomer interacts with a pseudo-symmetric half-site.

Repressor proteins - the monomers have a two-domain structure:

N-terminal domain: a 69 residue DNA-binding domain known as R1-69. It is a 5-helix bundle with helices 2 and 3 forming a helix-turn-helix motif.
C-terminal domain: the domain mediates dimerization.

434 Cro protein - a single domain protein with a homologous structure to R1-69. Helices 4 and 5 provide ...

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Cro and Repressor are part of the lysogenic/lytic growth switch mechanism in bacteriophage and function through transcription regulation at operons.

DNA binding is conducted as a homodimer. Each monomer interacts with a pseudo-symmetric half-site.

Repressor proteins - the monomers have a two-domain structure:

N-terminal domain: a 69 residue DNA-binding domain known as R1-69. It is a 5-helix bundle with helices 2 and 3 forming a helix-turn-helix motif.
C-terminal domain: the domain mediates dimerization.

434 Cro protein - a single domain protein with a homologous structure to R1-69. Helices 4 and 5 provide part of the dimer interface.

Proteins bind to 6 related operator sites (named OL1-3 and OR1-3) with varying affinities. Each site is 14 bp with 4-conserved bp at either end. The central 6 bp modulate protein-binding affinity.

Helix 3 makes base contacts in the major groove while helix 2 and the helix 2/3 turn bind the DNA backbone.

The CRO Repressor protein is involved in stopping the transcription of certain genes.

Cro, a repressor protein of temperate bacteriophages (e.g. lambda), works in opposition to the phage's repressor to control the genetic switch that determines whether a lytic or lysogenic cycle will follow infection. When phage DNA enters a new bacterial host cell, the beginning of both a lytic and lysogenic infection is initiated by the expression of the immediate early and delayed early genes of the phage. A competition between the cro and repressor proteins ensues, the outcome of which determines whether the phage embarks on a lytic or lysogenic lifecycle.

Cro and repressor compete for control of an operator region containing three operators that determine the state of the lytic/lysogenic genetic switch. If repressor wins this competition, transcription of the cro gene is blocked and repressor synthesis is maintained. Lysogeny will result. A competition won by cro, however, means that the late genes of phage l will be expressed; this will result in lysis. In this case, cro blocks transcription that occurs from Prm, the promoter that is responsible for the maintenance of repressor transcription.