Label and sketch the four common protein motifs found in tra

Label and sketch the four common protein motifs found in transcriptional regulators of eukaryotic promoters, using the space below. Show what region of the protein binds to DNA. List a gene or type of gene that is controlled by each of these proteins.

Solution

Answer:

Four common protein motifs found in transcriptional regulators of eukaryotes are:

1. Helix turn helix motif -

A related helix turn helix motif is found in the homeodomain found in the developmental regulation in Drosophila. The specificity of DNA recognition and interaction lies within the homeodomain. It is also found in genes coding for mammalian transcription factors.

2. Zinc finger motif -

It is found in TFIIIA involved in transcription of 5s rRNA genes by RNA Polymerase III. The c-terminal part of the zinc finger motif forms a-helices which recognizes and binds to DNA.

3. Leucine zipper motif -

A stretch of amino acids form the leucine zipper with the leucine residues providing the surface for dimerization. Dimerization opens up sites for binding to DNA. The residues adjacent to the leucine repeats are basic and provides a DNA binding site. C/EBP containing this motif binds as a dimer to both the CAAT box and the SV40 core enhancer. Proteins containing leucine zippers control apical formation during embryogenesis.

4. Helix loop helix motif -

Helix loop helix motif contain a region adjacent to the helix loop helix comprising of basic residues that help in DNA binding. Mammalian MyoD and myogenin containing the helix loop helix motif are involved in myogenesis (also called myogenic regulatory factors).