CHARACTERIZATION OF A CDNA-ENCODING A NOVEL PLANT POLY(A) POLYMERASE

We have isolated cDNA clones encoding a novel factor (PAP-I) that is a component of a multi-subunit poly(A) polymerase from pea seedlings. T he encoded protein, when isolated from appropriately engineered Escher ichia coli, was active as a poly(A) polymerase, either with an associa ted RNA binding cofactor (PAP-III) or with free poly(A) as an RNA subs trate. The latter observation indicates that PAP-I is in fact a poly(A ) polymerase, PAP-I bore a striking resemblance to an as yet uncharact erized cyanobacterial protein. This observation suggested a possible c hloroplast localization for PAP-I. This hypothesis was tested and foun d to be substantiated; immunoblot analysis identified PAP-I in chlorop last but not nuclear extracts. Our results suggest that PAP-I is a com ponent of the machinery that adds poly(A) to chloroplast RNAs.