One RNA polymerase serving two genomes

The land plant Arabidopsis thaliana contains three closely related nuclear genes encoding phage-type RNA polymerases (RpoT;1, RpoT;2 and RpoT;3). The gene products of RpoT;1 and RpoT;3 have previously been shown to be importe d into mitochondria and chloroplasts, respectively. Here we show that the t ransit peptide of RpoT;2 possesses dual targeting properties. Transient exp ression assays in tobacco protoplasts as well as stable transformation of A rabidopsis plants demonstrate efficient targeting of fusion peptides consis ting of the N-terminus of RpoT;2 joined to green fluorescent protein to bot h organelles. Thus, RpoT;2 might be the first RNA polymerase shown to trans cribe genes in two different genomes. RNA polymerase activity of recombinan t RpoT;2 is uneffected by the inhibitor tagetin, qualifying the gene produc t of RpoT;2 as a phage-type polymerase.