Fundamental Mechanisms of Ion Channel Proteins 
bilized state and are performing conventional 
membrane purification studies. The channel is 
expressed in its natural tissue at high density, so 
milligram quantities should be easily obtained. 
The isolation of this channel will enable us to 
study the molecular family of voltage-dependent 
anion channels at the protein-biochemical level. 
-Structure-Function Relations in a Minimal 
K+ Channel 
We are beginning a structure-function analysis 
on a K^-specific channel, first cloned from a kid- 
ney cDNA library, that shows a remarkable molec- 
ular property: a very small polypeptide size of 
only 130 amino acids, some 1 0-fold smaller than, 
for example, the voltage-dependent Na"^ channel. 
We have constructed and expressed a fully syn- 
thetic gene for this channel, using the degeneracy 
of the genetic code to build a large number of 
unique restriction sites throughout the coding se- 
quence. Thus prepared to perform routine cas- 
sette mutagenesis, we are initiating a search for 
functional domains of the channel and develop- 
ing direct tests to determine whether this gene 
does in fact code for an ion channel at all, a basic 
question that has yet to be answered rigorously. 
We have found point mutations in the single 
hydrophobic domain that specifically alter ion se- 
lectivity among close analogues as well as the 
affinities of several channel blockers. The results 
not only demonstrate that this cDNA does code 
for a structural gene for a channel but also 
provide initial intimations about the way the Re- 
conducting pore is formed. 
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