Oligomeric proteins containing N-terminal targeting signals are imported into peroxisomes in transgenic Arabidopsis

Employing transgenic Arabidopsis plants, we analyzed the mechanism for the translocation of peroxisomal proteins from the cytosol into the matrix that is mediated by the N-terminal targeting signal. A hybrid Arabidopsis variety was generated which accumulates two kinds of originally bacterial proteins, P-glucuronidase (GUS) and a GUS chimeric protein designated as CS-Delta C42-GUS, that carries the N-terminal targeting signal for glyoxysomal citrate synthase. Because the CS-Delta C42-GUS is targeted to peroxisomes but had never been observed to be processed to produce the mature protein, it can be distinguished from the GUS protein by its molecular size. Cell fractionation analyses showed that the native GUS protein, although lacking the targeting signal, was co-localized with the CS-Delta C42-GUS protein in the peroxisomes of the hybrid plant. It is suggested that the native GUS protein forms oligomeric structures with the peroxisome-targeted chimeric proteins and can therefore be transported into peroxisomes. Sucrose density gradient centrifugation revealed that the native GUS and the chimeric GUS indeed are present both as a dimer and a tetramer in the Arabidopsis hybrid variety.