Characterization of Oryza sativa telomerase reverse transcriptase and possible role of its phosphorylation in the control of telomerase activity.
Telomerase reverse transcriptase (TERT) has been characterized in the dicotyledon Arabidopsis thaliana. A TERT homolog has now been identified in the monocotyledon rice (Oryza sativa L.) on the basis of its predicted homology to the A. thaliana enzyme (AtTERT). At least five alternatively spliced transcripts of the rice TERT (OsTERT) gene were detected. The full-length OsTERT protein shares structural features with TERTs of other species, including a calculated molecular size of 144 kDa, an isoelectric point of 9.6, and conserved sequence motifs. Phylogenetic analysis showed that OsTERT clusters with AtTERT and is more related to the human and mouse enzymes than to those of yeast and ciliated protozoa, consistent with the evolutionary relations among these eukaryotes. Telomerase activity was abundant in shoot apices and cultured cells but was low or absent in leaves or roots of rice plants, whereas similarly spliced OsTERT transcripts were detected in all tissues examined and cultured cells. Similar to mouse and human TERT proteins, OsTERT contains two putative phosphorylation sites for Akt kinase. Incubation of a rice cell extract with Akt or with protein phosphatase 2A potentiated or inhibited telomerase activity, respectively, whereas Akt did not affect the activity in Arabidopsis cell extract. In addition, the kinase activated the telomerase in a leaf extract. The mechanism of telomerase regulation in rice thus appears to differ from that in Arabidopsis (which is mediated predominantly at the level of AtTERT transcription), possibly reflecting the taxonomic distance between monocotyledons and dicotyledons.
Oguchi
Keiko
K
Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Tamura
Katsunori
K
Takahashi
Hideo
H
D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D004268:DNA-Binding Proteins; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D010802:Phylogeny; D010936:Plant Extracts / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012326:RNA Splicing; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D010936:Plant Extracts; D010940:Plant Proteins; D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C509186:TERT protein, human; D019098:Telomerase; C509187:Tert protein, mouse; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2