THE NUCLEAR RPL4 GENE ENCODES A CHLOROPLAST PROTEIN THAT COPURIFIES WITH THE T7-LIKE TRANSCRIPTION COMPLEX AS WELL AS PLASTID RIBOSOMES

We have cloned and sequenced the cDNA and the gene coding for plastid ribosomal protein L4 (RPL4) from two higher plant species, spinach and Arabidopsis thaliana. Ribosomal protein L4 is one of the ribosomal pr oteins far which extraribosomal functions in transcriptional regulatio n has been demonstrated in prokaryotes, Sequence comparison of the two plant cDNAs and genes shows that the RPL4 gene has acquired a remarka ble 3' extension during evolutionary transfer to the nuclear genome. T his extension harbors an intron and codes for a glutamic and aspartic acid-rich amino acid sequence that resembles highly acidic C-terminal tails of same transcription factors, Co-purification of ribosomal prot ein L4 with plastid RNA polymerase and transcription factor CDF2 using different purification protocols as well as the surprising amino acid sequence of the L4 protein make it a likely candidate to play a role in plastid transcriptional regulation.