Question

1. The protein REST is a transcription factor that repressesthe expression of neuronal genes (genes only expressed in neurons). Predict whether REST would be found bound to the promoter of each gene in the designated tissue (think about whether they are expressed in each tissue). Write a “+” for located at the promoter and a “-“ for not located at the promoter.

	Brain	Muscle
Nav
HK1 (hexokinase)
RPL1 (ribosome protein)
Kv

Answer 1

Nav is a Na-gated Voltage channel that is responsible for the depolarization of neurons during an action potential. Hence, this gene is present in the brain. Also, it is present in muscle tissues, where entry of Na+ ions triggers the membrane to depolarize and undergo contraction. Hence, this gene is not specific to neurons and should not be suppressed in either brain or in muscle. Thus, REST inhibitor should not be located at the promoter of this gene in either tissues.

HK1 or Hexokinase 1 is the gene that is responsible for trapping the glucose after it enters the cell. It does so by phosphorylating it. This prevents the exit of glucose from the cell, thereby allowing the cell to sequester glucose and feed it into the glycolytic pathway. Glycolysis is very high in brain. However, muscle cells also metabolize glucose. Hence, the gene is present in both the brain and muscle. Therefore, it should not be inhibited by REST in either of the tissues.

RPL1 is a ribosomal protein and is essential for ribosomal assembly and translation. Since translation of proteins by the ribosomal complexes is seen in both the brain and the muscle tissues, the protein expression is not inhibited by REST in either of the tissues.

Kv is a potassium-gated voltage channel. Its role is in repolarizing the neurons following an action potential. The action potential is also seen in muscle tissues and hence Kv proteins are also localized on the muscle membrane. Thus, the gene is expressed in both the tissues, and hence REST should not inhibit the expression of Kv in either brain or muscle.

Summarizing, all the entries in the above table should be "-".