Characterization of the transcript of a new class of retroposon-type repetitive element cloned from the powdery mildew fungus, Erysiphe graminis.

The putative master transcript of a novel class of repetitive element has been cloned from the fungus erysiphe graminis f.sp. hordei. Sequence analysis of the cDNA revealed that the element, designated Eg-R1, is a member of the retroposon superfamily with properties in common with SINEs and LINEs (short or long interspersed elements). SINE-like properties include the transcript size (approximately 700 bp), and the lack of major open reading frames. In contrast, the fact that the transcript is polyadenylated and is most probably transcribed by RNA polymerase II, suggests a functional relationship to LINEs. Except for a short, but striking, sequence identity to a published SINE from the same fungus, no similar sequence was found in database searches. A constitutively high transcript level is found throughout the asexual life cycle of the fungus. Small differences in band patterns of Southern blots were observed between two isolates of E. graminis f.sp. hordei, while the band patterns in an isolate of the very close relative E. graminis f.sp. tritici in general appear dissimilar. This may imply that the element is currently active. Recent dispersal is confirmed by the observation that an approximately 550 bp internal hinfI fragment is conserved in the majority of the copies in all three isolates. Approximately 50 copies are present in E. graminis f.sp. hordei.