Characterization of a cDNA clone encoding a chloroplast-targeted Clp homologue

Efforts to identify cDNA clones encoding chloroplastic envelope membrane proteins of Pisum sativum L. led to the isolation of a clone encoding a 92 kDa protein found in both the inner envelope membrane and the soluble fraction of chloroplasts. Sequential transcription and translation from the insert of this clone yielded a 102 kDa protein that could be imported into chloroplasts and processed to a 92 kDa form. Although the protein was identified because it reacted with antibodies to chloroplastic envelope proteins, the imported 92 kDa protein was recovered primarily in the soluble fraction of chloroplasts. The deduced amino acid sequence of this protein has strong similarity to the Clp proteins, a recently described family of highly conserved proteins present in all organisms examined to date. The physiological significance of the presence of this protein in chloroplasts is discussed.