35S-radiolabeled precursor proteins, plasmids carrying a SP6
promoter-binding region followed by the gene of interest were used. Plasmids
were incubated with the TNT SP6 quick coupled kit (Promega), an in
vitro eukaryotic transcription/ translation system based on
rabbit reticulocytes, and [35S] methionine (PerkinElmer) for 2 hr
at 30°C and 300 rpm.
For the in vitro translation of
[35S]Por1 the Rabbit Reticulocyte Lysate System (Promega) was
used. First, mRNA was synthesized by using the mMESSAGE mMACHINE SP6 kit
(Invitrogen) and cleaned up by the MEGAclear Transcription Clean-Up kit
(Invitrogen). Radiolabeled proteins were translated by using the Rabbit
Reticulocyte Lysate System (Promega) for 2 hr at 30°C and 300
rpm.
After translation, 20 mM unlabeled methionine (Roth) and 0.3 M
sucrose (MP Biomedicals) were added. Lysate was snap frozen in liquid
nitrogen and stored at –80°C.