UASt regulatory sequences drive expression of mRFP(Unk) that is tagged at the N-terminal end with a Tag:Mito(mAkap1) mitochondrial localization signal and at the C-terminal end with a Tag:ER(yUBC6) endoplasmic reticulum localization sequence. This results in a protein that can be used to tighten the physical coupling between the ER and mitochondria, with the mRFP(Unk) protein acting as a linker (as well as being fluorescent); the maximum length of the protein, based on the size of mRFP(Unk) is calculated to be less than 5nm.