Deletion analysis of K+ channel assembly.

An understanding of K+ channel structure is a critical step in developing an appreciation of the function and regulation of these proteins. We have begun a biochemical analysis of the early steps in K+ channel formation following translation into endoplasmic reticulum membranes. In our experiments, a series of K+ channel subunit protein deletions were constructed and then tested for posttranslational processing and assembly. We find that all deletions containing the S1 domain are inserted into the membrane. The loop between S1 and S2 is glycosylated; thus, this segment is topologically extracellular. Translated subunit proteins mix in the membrane, then assemble into tetramers. This subunit assembly is critically driven by a conserved, self-tetramerizing sequence in the N-terminal cytoplasmic region, which we have named the tetramerization 1 domain.