The I-SK (also called minK) protein, although it is structurally unrelated to any other ion channel subunit, induces slowly activating, voltage-dependent Kt channels (I-minK) in Xenopus oocytes or HEK293 cells. The quaternary structure of the I-minK channel complex has long remained a mystery, but recent studies suggest an interaction of the I-SK protein with a traditional K+ channel subunit, identified in man as K(V)LQT1. It is unclear at this point what the mechanism of this interaction is, or whether the I-SK protein may also interact with other ion channel subunits. However, there is an abundance of information regarding the role and regulation of the I-SK protein in the I-minK channel complex, discussed in this review by Andreas Busch and Hartmut Suessbrich. The I-SK protein is expressed in different tissues, where I-minK activation may have distinct net effects on cell function. This fact makes I-minK an excellent target for pharmacological agents.