IN-VIVO ADDITION OF TELOMERIC REPEATS TO FOREIGN DNA GENERATES EXTRACHROMOSOMAL DNAS IN THE TAXOL-PRODUCING FUNGUS PESTALOTIOPSIS-MICROSPORA

Transformation of the taxol-producing filamentous fungus Pestalotiopsi s microspora with a plasmid containing the bacterial hygromycin resist ance gene fused to Aspergillus regulatory sequences resulted in the in vivo formation of extrachromosomal DNAs with telomeric repeats in the majority of transformants. Repeats of the telomeric sequence 5'-TTAGG G-3' were appended to nontelomeric transforming DNA termini, No fungal sequences other than telomeric repeats were detected in extrachromoso mal DNAs. Transformants contained three to six different sizes or conf ormational forms of extrachromosomal DNAs. The DNAs showed no change i n size or internal structure during 6 months of growth with selection, but were lost after 20 days of growth without selection. Transformati on of wild-type P. microspora with a PCR-amplified extrachromosomal DN A having terminal telomeric repeats produced up to 50-fold more transf ormants than the original transformation vector. The addition of telom eric repeats to foreign DNA is unusual among fungi and may have import ant adaptive or developmental implications. (C) 1998 Academic Press.