The Mitochondrial LSU rRNA Group II Intron of Ustilago maydis Encodes an Active Homing Endonuclease Likely Involved in Intron Mobility
(A) Schematic of the polymorphic region within the LSU rDNA of U. maydis. Depicted are the parental W and F types and the recombinant X1 type. Boxes refer to deduced exon sequences (the three major ones are numbered from I to III). Stippled lines connect homologous sequences. All numbers refer to the complete mitochondrial genome sequence of U. maydis strain 521. Black arrows mark predicted HEGs within intronic regions (termed LRI1, LRI2, LRI3 and LRII1). LRII1 and I-UmaI are marked in red. The schematic (drawn to scale) is adapted from Fedler et al.  with permission of the Genetics Society of America. (B) The schematic shows the target cleavage site (red, bold face type) within the recipient F type sequence (indicated positions refers to the mitochondrial genome sequence of strain 521; see part A). The staggered line (stippled) marks produced 3′ overhangs. The upper part shows the donor sequence of the W type interrupted by intron LRII1. Crosses refer to potential homologous recombination events.