title: Expression of the telomeric repeat binding factor gene NgTRF1 is closely coordinated with the cell division program in tobacco BY-2 suspension culture cells.
abstract: Telomeres are vital for preserving chromosome integrity during cell division. Several genes encoding potential telomere-binding proteins have recently been identified in higher plants, but nothing is known about their function or regulation during cell division. In this study, we have isolated and characterized a cDNA clone, pNgTRF1, encoding a putative double-stranded telomeric repeat binding factor of Nicotiana glutinosa, a diploid tobacco plant. The predicted protein sequence of NgTRF1 (Mr = 75,000) contains a single Myb-like domain with significant homology to a corresponding motif in human TRF1/Pin2 and TRF2. Gel retardation assays revealed that bacterially expressed full-length NgTRF1 was able to form a specific complex only with probes containing three or more contiguous telomeric TTTAGGG repeats. The Myb-like domain of NgTRF1 is essential, but not sufficient, to bind the telomeric repeat sequence. The glutamine-rich extreme C-terminal region, which does not exist in animal proteins, was additionally required to form a specific telomere-protein complex. The dissociation constant (Kd) of the Myb motif plus the glutamine-rich domain of NgTRF1 to the two-telomeric repeat sequence was evaluated to be 4.5 +/- 0.2 x 10-9 m, which is comparable to that of the Myb domain of human TRF1. Expression analysis showed that NgTRF1 gene activity was inversely correlated with the cell division capacity of tobacco root cells and during the 9-day culture period of BY-2 suspension cells, while telomerase activity was positively correlated with cell division. In synchronized BY-2 cells, NgTRF1 was selectively expressed in G1 phase, whereas telomerase activity peaked in S phase. These findings suggest that telomerase activity and NgTRF1 expression are differentially regulated in an opposing fashion during growth and cell division in tobacco plants. The possible physiological functions of NgTRF1 in tobacco cells are also discussed.
authors.affiliation: Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea.
authors.forename: Seong Wook
authors.initials: SW
authors.lastname: Yang
authors.forename: Dong Hyun
authors.initials: DH
authors.lastname: Kim
authors.forename: Jai Jin
authors.initials: JJ
authors.lastname: Lee
authors.forename: Yoon Joo
authors.initials: YJ
authors.lastname: Chun
authors.forename: Jae-Hyeok
authors.initials: JH
authors.lastname: Lee
authors.forename: Yun Ju
authors.initials: YJ
authors.lastname: Kim
authors.forename: In Kwon
authors.initials: IK
authors.lastname: Chung
authors.forename: Woo Taek
authors.initials: WT
authors.lastname: Kim
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D001667:Binding, Competitive; D015152:Blotting, Northern; D015139:Blotting, Southern; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D016193:G1 Phase; D017353:Gene Deletion; D005786:Gene Expression Regulation; D015723:Gene Library; D049452:Green Fluorescent Proteins; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009693:Nucleic Acid Hybridization; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D016196:S Phase; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013347:Subcellular Fractions; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D035321:Telomeric Repeat Binding Protein 1 / Q000096:biosynthesis* / Q000235:genetics*; D013997:Time Factors; D014026:Nicotiana / Q000235:genetics*
chemical_list: D018076:DNA, Complementary; D008164:Luminescent Proteins; D012333:RNA, Messenger; D035321:Telomeric Repeat Binding Protein 1; D049452:Green Fluorescent Proteins; D004247:DNA; D019098:Telomerase; D007213:Indomethacin