Question

1.Summarize four different types of DNA –protein interactions and their functional consequences using the table below.

#	Type of DNA-protein interaction	Functional Consequences
1
2
3
4

Answer 1

DNA-protein interactions can be specific or non-specific. Specific interactions take place by means of specialized domains which are found in interacting proteins such as transcription factors. Some of the domains involved in DNA-protein interactions are:

1) Helix-turn-helix - This motif consists of two alpha helices seprated by a short (four amino acid) peptide sequene that forms a beta turn. Transcription factors which play an important role in early embryo development in Drosophila contain this motif.

2) Zinc finger - The zinc finger is a loop of 12 amino acids with two cysteines and two Histidines at the base of the loop that tetrahedrally coordinate a Zinc ion.TFIIIA contain Zinc fingers.

3) Leucine zippers - This motif contains a leucine every seventh amino acid in the primary sequence and forms an alpha helix with the leucines presented on the same side of the helix every second turn, giving a hydrophobic surface.

4) Activation domains - There are certain domains of amino acids which are not sequence specific DNA binding domain but carry out some function. Glutamine-rich domains for example are found in SP1 transcription factors.