Abstract
High levels of a family of proteins called pokeweed antiviral protein (PAP) are found in various organs ofPhytolacca americana. Polymerase chain reaction (PCR) amplification of genomic DNA fromPhytolacca americanawas used to clone and sequence the genomic genetic determinants of three members of the PAP family: PAP I, PAP II, and PAP-S. The results demonstrated that PAP I and PAP-S do not contain an intron, whereas one PAP II gene is composed of two exons separated by an intron of 734 basepairs in length. Since the amino acid sequence of PAP II is only 33% similar to PAP I and PAP-S, and since it seems unlikely that an intron has been inserted into a pre-existing gene, the PAP II gene could be the ancestor of the PAP family. Interestingly, PAP II expression is regulated differently in leaf and seed tissues and is the only PAP transcript which increases progressively with plant aging. The evolutionary relationship of PAPs could help to identify relevant functional structures of these proteins and shed new light on structural functional models which attempt to explain their enzymatic action.
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