For these experiments, we fused eCFP and eYFP (individually) to the amino-terminal end of CNGB1-∆N (eCFP-CNGB1-∆N and eYFP-CNGB1-∆N respectively). The eCFP and eYFP fusion constructs exhibited functional properties indistinguishable from their non-fusion counterparts (data not shown). As the amino-terminal region is deleted in this subunit, the fluorescent proteins should be near the inner leaflet of the membrane, close to the S1 transmembrane segment. Based on the structure of the related Kv1.2 channel 26 , two fluorescent proteins in the same channel should be about 56 Å apart (assuming they are in adjacent subunits) or 79 Å apart (assuming they are in nonadjacent subunits).