Abstract
NOG1 is a nuclear GTP-binding protein which is conserved among archaea and eukaryotes (including animals, plants and fungi). It has been shown that NOG1 homologues are involved in early steps of 60S ribosomal biogenesis in nucleus of Trypanosoma, yeast and mouse. Here we characterized the plant Nog1 protein in Arabidopsis. Arabidopsis has three NOG1 homologues, named AtNOG1-1, AtNOG1-2 and AtNOG1-3, but only NOG1-1 is constitutively expressed in all the tissues examined. Actually AtNOG1-1 seems to be essential for plant development. AtNOG1-1 is directed to nucleolus and nucleoplasm. FRAP analysis revealed that the distribution of NOG1-1 protein between nucleolus and nucleoplasm was sensitive to transcription and translation inhibitors, also carbon and nitrogen starvation, suggesting its role in early steps of ribosomal biogenesis. NOG1-1 shows a dynamic behavior during mitosis. The NOG1-1 protein disappeared in pre-metaphase, and is rapidly re-accumulated in peripheral chromosomal region in early anaphase. We also found a novel and plant-specific sub nucleolar structure named "nog1 body" which appears in nucleus region during late anaphase and early telophase.
