Identification of group-I introns at three different positions within the 28S rDNA gene of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae.

Using a set of heterologous primers designed from the 3'-end of the 28S rRNA gene of Verticillium dahliae the corresponding gene region of 30 isolates of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae was amplified. The polymerase chain reaction products obtained could be classified into four groups varying in size from 1.0 to 2.2 kb. Sequence analyses of representative PCR products revealed the presence of five distinct introns, positioned in three different insertion sites. Fungal isolates 316 and 11 both harbored one intron each (374 and 337 bp in size, respectively), whereas isolate 33 harbored three introns (436, 334, and 412 bp) within the relevant 28S rRNA region. All five introns shared the conserved P, Q, R, S elements and all the other characteristic features of group-I introns in their deduced secondary structure; three (316-int, 33-int1, and 33-int3) belong to subgroup IC1 and two (33-int2 and 11-int) belong to subgroup IE. Further, reverse transcription polymerase chain reactions indicated that all these introns were absent from the mature RNA molecules. The appearance of the five introns at identical positions with those from other organisms belonging to various phyla is discussed.