2 TANDEMLY REPEATED TELOMERE-ASSOCIATED SEQUENCES IN NICOTIANA-PLUMBAGINIFOLIA

Two tandemly repeated telomere-associated sequences, NP3R and NP4R, ha ve been isolated from Nicotiana plumbaginifolia. The length of a repea ting unit for NP3R and NP4R is 165 and 180 nucleotides respectively. T he abundance of NP3R, NP4R and telomeric repeats is, respectively, 8.4 x 10(4), 6 x 10(3) and 1.5 x 10(6) copies per haploid genome of N. pl umbaginifolia. Fluorescence in situ hybridization revealed that NP3R i s located at the ends and/or in interstitial regions of all 10 chromos omes and NP4R on the terminal regions of three chromosomes in the hapl oid genome of N. plumbaginifolia. Sequence homology search revealed th at not only are NP3R and NP4R homologous to HRS60 and GRS, respectivel y, two tandem repeats isolated from N. tabacum, but that NP3R and NP4R are also related to each other, suggesting that they originated from a common ancestral sequence. The role of these repeated sequences in c hromosome healing is discussed based on the observation that two to th ree copies of a telomere-similar sequence were present in each repeati ng unit of NP3R and NP4R.