Characterization of the matK Gene in the Poaceae

The matK gene is named according to its possible maturase function and its location within the trnK gene encoding the tRNA (UUU). A 509 open reading frame was found to reside in an intron when the trnK gene was sequenced in tobacco (Nicotiana tabacum) (Sugita et al., 1985). Later, a complete sequence of the liverwort Marchantia polymorpha confirmed the existence of this open reading frame in the non-vascular plant, although it is short compared to those in other plants (Ohyama et al., 1986). Neuhaus and Link (1987) suggested the possible maturase function of the matK gene in mustard (Sinapis alba), based upon their homology search result. A segment near the carboxyl terminus of the derived mustard trnK polypeptide is structurally related to the portions of maturase-like polypeptides of introns of the mitochordrial cytochrome c oxidase subunit I gene (COXI) of yeast (Saccharomyces cerevisiae) and ascomycete (Podospora anserina). The maturase MatK presumably helps fold the intron RNA into the catalytically-active structure. Thereafter, the matK gene was sequenced from various plants, such as rice (Oryza sativa), two pine species (Pinus contrta and P. thunbergii), and beechdrop (Epifagus virginiana) (Hiratsuka et al., 1989; Lidholm and Gustafsson, 1991; Wolfe et al., 1992). In beechdrop, this open frame appeared as a freestanding gene with neither the trnK exons nor the interrupting introns present.