ISOLATION AND CHARACTERIZATION OF A CDNA CLONE ENCODING THE POKEWEED ANTIVIRAL PROTEIN-II FROM PHYTOLACCA-AMERICANA AND ITS EXPRESSION IN ESCHERICHIA-COLI

Three distinct ribosome-inactivating proteins (RIPs) were isolated fro m 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. T he cDNA of PAP II consists of 1,187 nucleotides and encodes a mature p rotein of 285 amino acids. Its predicted amino acid sequence is only 3 3% similar to PAP and PAP-S. The NH2 terminal extrapeptide (25 amino a cid residues) was similar but not identical to that of PAP's extrapept ide. The cDNA of PAP II was expressed in E. coli. The growth of the tr ansformants was strongly inhibited after induction of the gene. Furthe rmore, PAP II, which was produced in E. coli, inhibited protein synthe sis in a rabbit reticulocyte translation system. Thus, recombinant PAP II would appear to be as functional as native PAP in inhibiting prote in synthesis in both prokaryotes and eukaryotes.