J. Plant Res. 110: 495-499, 1997 Short Communication Journal of Plant Research ~) by The Botanical Society of Japan 1997 A Full Length Ty3/gypsy-Type Retrotransposon in the Fern Adiantum Kazunari Nozue, Takeshi Kanegae and Masamitsu Wada* Department of Biology, Faculty of Science, Tokyo Metropolitan University, Minami Osawa 1-1, Hachioji-shi, Tokyo, 192-03 Japan Ty3/gypsy-type LTR-retrotransposons have been found only in lily and maize but not in cryptogam. In fern Adlanturn, we recently found a full-length Ty3/gypsy- type LTR-retrotransposon (ARET-1; 8284bp). This retrotransposon has both 5' and 3' LTRs (1.2 kb), a primer binding site, a polypurine tract, and an RNA binding motif and its domain arrangement in the pol region is the same as that of Ty3/gypsy-type retrotrans- poson. These results suggest that Ty3/gypsy-type retrotransposons are widespread among vascular plants. Key words: Adiantum ~ ARET-1 ~ Fern m Phyto- chrome-- Retrotransposon m Ty3/gypsy Retrotransposons are mobile DNA elements which inte- grate into chromosomes after reverse transcription of element-encoded RNA and are thoLight to contribute to host genome organization because of their great abun- dance, widespread occurrence, and hypervariability (Ben- netzen 1996). One type of retrotransposon which has long terminal repeats (LTRs) is found in yeasts, animals, and plants, and is divided into two groups, Tyl/copia and Ty3/gypsy. The broad phylogenetic distribution of the former type of LTR-retrotransposon has been well documented from the alga Volvox to the ferns Equisetum and Osmunda and to seed plants (Voytas et al. 1992). Until now, Ty3/gypsy retrotransposons have only been found in seed plants, Lilium (del 1-46) (Smyth et al. 1989) and Zea (Purugganan and Wessler 1994, SanMiguel et al. 1996). Here we report the identification and characteriza- tion of full-length Ty3/gypsy-type retrotransposon in the non-seed plant, maidenhair fern Adiantum capillus-vener- is, and present structural characteristics of this retrotrans- poson. During the course of screening and sequencing of genes of Adiantum phytochromes (red/far-red light absorbing chromoprotein in plants (reviewed in Kendrick and Kronenberg (1994), Wada et al. (1997)), we isolated a Abbreviations: LTR, long tem~inal repeat; PBS, primer binding site; PPT, polypurine tract The nucleotide sequence data reported will appear in the EMBL, DDBJ and GenBank Nucleotide Sequence Databases under the accession number AB003364. genomic clone, composed of a phytochrome-like sequence (Adiantum PHY4), that was followed by a full length LTR-retrotransposon (Figs. 1 and 2). A 13 kb Sail- Sail genomic DNA fragment containing both Adiantum PHY4 and Adiantum retrotransposon (ARET-I) was sub- cloned into a plasmid pBluescript II SK + and sequenced. Downstream of PHY4 exonl, we found an 1166 bp sequence containing 26 GA repeats followed by a full length retrotransposon. Full length ARET-1 is 8284 bp long (Fig. 2A). The 5' LTR and the 3' LTR are 1230 bp and 1232 bp in length, respectively, and they are 94.5% identical. An internal region adjacent to the 5' LTR possesses a primer binding site (PBS) which has 18 out of 25 bases complementary to the 3' end of the wheat tRNA Met (Ghosh et al. 1982) (Fig. 2B). The PBS is neces- sary for priming of (--) strand DNA synthesis from the RNA template of retrotransposon (Boeke and Corces 1989). Close to the 3' LTR there is a purine-rich region (AACA- GAAAAG), known as a polypurine tract (PPT), that is needed for the switch to (+) strand DNA synthesis (Boeke and Corces 1989). Taken together, ARET-1 has all domains and elements characteristic of retrotransposons. The existence of multiple stop codons in all three open reading frames suggested that the ARET-1 is not an active element. Among many known retrotransposons in plants, only tobacco Tntl and Ttol, rice Tos17, maize Zeon, and barley BARE-1 are known to be active (Grandbastien et al. 1989, Hirochika 1993, Hirochika et al. 1996, Hu et al. 1995, Suoniemi et al. 1996). 5'LTR Adiantum PHY4 PR In" RH IN m 3'LTR Adiantum ARET-1 1 kb Fig. 1. Schematic representation of structure of Adiantum PHY4 and retrotranst:x:~:~n (ARE/--/) and its domain organization. GAG, several structural proteins of the vifion core; PR, protease; RT, reverse transcriptase; la-I, RNase H; IN, integrase.