Bacterial 7-repressor

The lac repressor monomer, a chain of 360 amino acids, associates into a functionally active homotetramer. It is the classic member of a large family of bacterial repressors with homologous amino acid sequences. PurR, which functions as the master regulator of purine biosynthesis, is another member of this family. In contrast to the lac repressor, the functional state of PurR is a dimer. The crystal structures of these two members of the Lac I family, in their complexes with DNA fragments, are known. The structure of the tetrameric lac repressor-DNA complex was determined by the group of Mitchell Lewis, University of Pennsylvania, Philadelphia, and the dimeric PurR-DNA complex by the group of Richard Brennan, Oregon Health Sciences University, Portland. 

Does a bacterial repressor molecule bind to the promoter or operator site adjacent to a gene in DNA ... 

Fig. 7.7. Bacterial two-hybrid (B2H) systems increase the number of protein variants that can be tested in each selection. A. The first B2H systems were based on natural bacterial repressor proteins [50], In the example shown, protein X is fused to the C-terminal end of a 434 repressor-leucine (L) zipper fusion, which binds to the 434 operator. Occupation of the 434 operator does not effect binding of RNA Pol or transcription of the reporter gene (left). However, if protein X interacts with protein Y, then the A,-repressor fusion is recruited to the low-affinity X operator, preventing RNA Pol from binding to the promoter region and thus, repressing transcription of the reporter gene (right). B. In the AraC-LexA system, repression is based on DNA bending [54], The...

The helix-tum-helix motif (HTH motif) is - historically seen - the first DNA-binding motif whose structure could be solved in a complex with DNA. It is often found in bacterial repressors. Many eucaryotic DNA-binding proteins also utilize the helix-turn-... 

The DNA-blndlng activity of most bacterial repressors is modulated by small effector molecules (inducers). This allows bacterial cells to regulate transcription of specific genes in response to changes in the concentration of various nutrients in the environment. 

The principles of specific protein-DNA interactions were first discovered during the study of bacterial repressors. Many bacterial repressors are dimeric proteins in which an a helix from each monomer Inserts into a major groove in the DNA helix (Figure 11-20). This a helix is referred to as the recognition helix or sequence-reading helix because most of the amino acid side chains that contact DNA extend from this helix. The recognition helix that protrudes from the surface of bacterial repressors to enter the DNA major groove and make multiple, specific interactions with atoms in the DNA is usually supported in the protein structure in part by hydrophobic interactions with a second a helix just N-termlnal to it. This structural element, which is present in many bacterial repressors, is called a helix-turn-helix motif. 

Homeodomain Proteins Many eukaryotic transcription factors that function during development contain a conserved 60-residue DNA-binding motif that is similar to the helix-turn-helix motif of bacterial repressors. Called homeodomain proteins, these transcription factors were first identified in Drosophila mutants in which one body part was transformed into another during development (Chapter 15). The conserved homeodomain sequence has also been found in vertebrate transcription factors, including those that have similar master control functions in human development. 

The first bacterial repressor assay was developed in 1990 by Sauer and coworkers, who adapted a bacterial A transcriptional repressor system to... 

Soft rot symptoms produced by E. chrysanthemi consist of a disorganisation of parenchymatous tissues following the release of bacterial pectinolytic enzymes. The diverse enzymes do not contribute equally to the virulence on a given host and their implication may vary according to the host considered. For instance, inactivation of pelE, pelD, pelA or pern in strain 3937 considerably reduces the virulence on African violets while mutations in pelB or pelC remain ineffective [2]. Pectinolysis is regulated by the transcriptional repressor KdgR, inactive in the presence of pectic inducers. 

---