A Group I intron in the nuclear small subunit rRNA gene of Cryptendoxyla hypophloia, an ascomycetous fungus: Evidence for a new major class of Group I introns

The ascomycetous fungus Cryptendoxyla hypophloia contains an insertion of 4 33 base pairs in the genes encoding nuclear small subunit ribosomal RNA. Se condary structure analyses of the insert reveal characteristics indicative of a Group I intron, including elements P, Q, R, and S; however, the sequen ces of these conserved regions deviate significantly from recognized consen sus sequences for Group I introns. Principal-components analysis, based on 79 nucleotide positions from the conserved core sequences of 93 Group I int rons, identified 17 introns similar to that of C. hypophloia. This grouping , which includes inserts from phylogenetically diverse organisms, cannot re adily be classified in any previously recognized major group of Group I int rons. We propose the creation of a new group, IE, to accommodate these sequ ences, and discuss the evolutionary relationships between group IE and othe r major groups of Group I introns.