Abstract: Described is a novel in vitro method for obtaining and identifying proteins which, in their natural in vivo setting, are covalently modified after translation. To identify novel isoprenylated proteins for subsequent biochemical study, colony blots of a Glycine max cDNA expression library were ?.sup.3 H! farnesyl labeled in vitro. Proteins identified by this screen contained several different carboxy-termini that conform to consensus farnesylation motifs. These proteins included known farnesylated proteins (DnaJ homologs) and several novel proteins, two of which contained 6 or more tandem repeats of a hexapeptide having the consensus sequence ?E or G! ?G or P!EK?P or K!K. Expression library screening by direct labeling can thus be adapted to recover and identify isoprenylated proteins as well as proteins with other post-translational modifications.