I-ApeI: a novel intron-encoded LAGLIDADG homing endonuclease from the archaeon, Aeropyrum pernix K1

Over 50 introns have been reported in archaeal rRNA genes (rDNAs), a subset of which nests putative homing endonuclease (HEase) genes. Here, we report the identification and characterization of a novel archaeal LAGLIDADG-type HEase, I-ApeI, encoded by the ApeK1.S908 intron within the 16S rDNA of Aeropyrum pernix K1. I-ApeI consists of 222 amino acids and harbors two LAGLIDADG-like sequences. It recognizes the 20 bp non-palindromic sequence 5′-GCAAGGCTGAAAC↓TTAAAGG and cleaves target DNA to produce protruding tetranucleotide 3′ ends. Either Mn2+ or Co2+ can be substituted for Mg2+ as a cofactor in the cleavage reaction. Of the 20 bases within the minimal recognition site, 7 are essential for cleavage and are located at positions proximal to the cleavage sites