Maturase K (matK) is a plant plastidial gene,[1] although higher plants have it moved into the nuclear genome.[2] The protein it encodes is an organelle intron maturase, a protein that splices Group II introns. It is essential for in vivo splicing of Group II introns.[3] Amongst other maturases, this protein retains only a well conserved domain X and remnants of a reverse transcriptase domain.[4]