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Peroxisomes are organelles found in all eukaryotic cells. Peroxisomes import integral membrane proteins post-translationally, and PEX19 is a predominantly cytosolic, farnesylated protein of mammalian and yeast cells that binds multiple peroxisome membrane proteins and is required for their correct targeting/insertion to the peroxisome membrane. We report the characterisation of the Arabidopsisthaliana homologue of PEX19 which is a predominantly cytosolic protein. AtPEX19 is encoded by two genes (designated AtPEX19-1 and AtPEX19-2) that are expressed in all tissues and at all developmental stages of the plant. Quantitative real time PCR shows that AtPEX19-1 and AtPEX19-2 have distinct expression profiles. Using in vitro translation and co-immunoprecipitation AtPEX19-1 was shown to bind to the Arabidopsis peroxisomal membrane protein PEX10. Additionally, bacterially expressed recombinant AtPEX19-1 was able to bind a fusion protein consisting of the C-terminus of PEX10 and glutathione S-transferase in pull-down assays, thereby demonstrating that non-farnesylated AtPEX19 can interact with the C-terminus of AtPEX10. Purified recombinant AtPEX19-1 was analysed by gel filtration chromatography and was found to have a molecular weight consistent with it forming a dimer and a dimer was detected in Arabidopsis cell extracts that was slightly destabilised in the presence of DTT. Moreover, cross-linking studies of native AtPEX19 suggest that in vivo it is the dimeric species of the protein that preferentially forms complexes with other proteins. [ABSTRACT FROM AUTHOR]