Prosomes exist in plant cells too.

A 19S particle was purified from tobacco (Nicotiana rustica) leaf cells. Its density was determined as 1296 g/cm3 in Cs2SO4-DMSO gradients, indicating the presence of RNA and protein. Polyacrylamide gel electrophoresis (PAGE) revealed eight distinct proteins in the range of 20-30 kD and RNA in the range of 70-80 nucleotides. Electron microscopic examination showed the same raspberry-shaped structure with a central depression as described for prosomes. We conclude that tobacco 19S particles represent small cytoplasmic complexes, possessing biochemical and structural characteristics similar to the hither-to known prosomes of animal cells.