Protein methyltransferase activities in commercial in vitro translation systems

Protein arginine methylation is a well-known post-translational modification that has been shown to occur in rabbit reticulocyte in vitro translation lysates (RRL); however, it is not known whether this is a general feature of in vitro-produced proteins from other eukaryotic cell-free translation systems, particularly insect-derived lysates (ICL). Because methylation can affect protein localization, RNA binding and protein-protein interactions this may be of great importance as in vitro-produced proteins are often used in assays of protein function. Here, I report the presence of base-stable and base-labile methyltransferase activities in RRL, ICL and wheat germ in vitro extracts (WGE). Indeed, the presence of CARM1 in RRL and ICL and a class II protein arginine methyltransferase activity (PRMT5/7) is documented in all three systems. Additionally, the lysine methyltransferase that modifies eukaryotic elongation factor 1A (eEF-1A) was detected in ICL and WGE. Importantly, using a defined set of substrates under identical conditions I show that all three in vitro systems contain different complements of the various methyltransferases. These data suggest that three systems can be used in a complementary fashion to investigate the effect(s) of post-translational modification on protein function.