TELOMERASE ACTIVITY IN PLANT-CELLS

Telomerase is a ribonucleoprotein enzyme which elongates the G-rich st rand of telomeric DNA to compensate for the progressive reduction in i ts length due to incomplete replication of chromosome ends, which in h uman somatic cells leads to cell cycle arrest upon shortening of telom eres to a critical length, To examine the possible involvement of telo merase in metabolism of plant genetic material, we used cells of Nicot iana tabacum strain TBY-2, a stable long-term culture which has kept a constant pattern of restriction fragments from chromosome termini dur ing its 6 month period of cultivation in our laboratory, In a direct a ssay for telomerase, a 5' end-labeled plant telomeric oligonucleotide (5')(TTTAGGG)(6)(3') was elongated in a TBY-2 cell extract, showing a pausing pattern which is a characteristic feature of telomerases from other organisms, The elongation was inhibited by RNase A pretreatment of the extract, We conclude that plant cells possess telomerase which is used for maintenance of their telomeres.