Oligomerisation of the red fluorescent protein, DsRed, can interfere with the localisation and function of proteins to which it is fused. We demonstrate an approach that may help to reduce significantly the impact of oligomerisation on the biology of the protein fusion partner. Growth of yeast (Saccharomyces cerevisiae) cells expressing ATP synthase containing subunit gamma-DsRed fusion was compromised relative to control cells. Furthermore, ATP synthase was found to exist as oligomeric structures when isolated under conditions where monomers would normally be present. The compromised growth phenotype was partially reversed and the oligomerisation of the ATP synthase reduced when a non-fluorescent variant of DsRed not fused to another protein was targeted to the mitochondrion in addition to the gamma-DsRed fusion protein. This strategy may also be applicable to the reduction of unwanted interactions between fusion proteins that contain the normally dimeric fluorescent proteins HcRed or Renilla GFP. (C) 2002 Elsevier Science (USA). All rights reserved.