A set of homo-oligomeric standards allows accurate protein counting.

Techniques based on fluorescence microscopy are increasingly used to count proteins in cells, but few stoichiometrically well-defined standards are available to test their accuracy. A selection of bacterial homo-oligomers were developed that contain 10-24 subunits and fully assemble when expressed in mammalian cells, and they can be used to easily validate/calibrate molecular counting methods. The utility of these standards was demonstrated by showing that nuclear pores contain 32 copies of the Nup107 complex.