A cDNA for nuclear-encoded chloroplast translational initiation factor 2 from a higher plant is able to complement an infB Escherichia coli null mutant

Formation of the initiation translation complex containing the three initia tion factors, IF1, IF2, and IF3, tRNA(fMet), and GTP constitutes the earlie st event in the protein synthesis. IF2, a GTP-binding protein, is the princ ipal factor involved in selecting and binding fMet-tRNA(fMet) the 30 S ribo somal subunit. Although some chloroplast initiation translational factors h ave been identified and purified from algae, none of these factors have bee n characterized from plants. In this work, we report the molecular characte rization of a nuclear-encoded chloroplastic IF2 gene from common bean (PvIF 2cp). We show that the PvIF2cp gene encodes a protein containing a chloropl ast translocation signal peptide, able to target a green fluorescent protei n fusion protein to chloroplasts. A high accumulation of PvIF2cp transcript was found in photosynthetic tissues, whereas low mRNA levels were detected in etiolated plants and in nonphotosynthetic organs. Additional data indic ate that the PvIF2cp transcript accumulation is modulated by light. The PvI F2cp gene encodes a functional factor, since the PvIF2cp conserved region, containing the G-domain and the C-terminal end, complements an Escherichia coli infB null mutation. Phylogenetic analysis using the PvIF2cp conserved region suggests that the PvIF2cp gene originated via endosymbiotic gene tra nsfer to the nucleus and that it may be a useful marker for phylogeny recon struction.