Isolation and characterization of a cDNA clone encoding the pokeweed antiviral protein II from Phytolacca americana and its expression in E. coli.

Three distinct ribosome-inactivating proteins (RIPs) were isolated from pokeweed (Phytolacca americana). We identified and sequenced for the first time a complete cDNA encoding the pokeweed antiviral protein II (PAP II), which is expressed in the late summer leaves of pokeweed. The cDNA of PAP II consists of 1,187 nucleotides and encodes a mature protein of 285 amino acids. Its predicted amino acid sequence is only 33% similar to PAP and PAP-S. The NH2 terminal extrapeptide (25 amino acid residues) was similar but not identical to that of PAP's extrapeptide. The cDNA of PAP II was expressed in E. coli. The growth of the transformants was strongly inhibited after induction of the gene. Furthermore, PAP II, which was produced in E. coli, inhibited protein synthesis in a rabbit reticulocyte translation system. Thus, recombinant PAP II would appear to be as functional as native PAP in inhibiting protein synthesis in both prokaryotes and eukaryotes.