Interaction between Agrobacterium tumefaciens oncoprotein 6b and a tobacco nucleolar protein that is homologous to TNP1 encoded by a transposable element of Antirrhinum majus

College of Bioscience and Biotechnology, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan.
Journal of Plant Research (Impact Factor: 1.82). 08/2008; 121(4):425-33. DOI: 10.1007/s10265-008-0160-1
Source: PubMed

ABSTRACT When gene 6b on the T-DNA of Agrobacterium tumefaciens is transferred to plant cells, its expression causes plant hormone-independent division of cells in in vitro culture and abnormal cell growth, which induces various morphological defects in 6b-expressing transgenic Arabidopsis thaliana and Nicotiana tabacum plants. Protein 6b localizes to the nuclei, a requirement for the abnormal cell growth, and binds to a tobacco nuclear protein called NtSIP1 and histone H3. In addition, 6b has histone chaperone-like activity in vitro and affects the expression of various plant genes, including cell division-related genes and meristem-related class 1 KNOX homeobox genes, in transgenic Arabidopsis. Here, we report that 6b binds to a newly identified protein NtSIP2, whose amino acid sequence is predicted to be 30% identical and 51% similar to that of the TNP1 protein encoded by the transposon Tam1 of Antirrhinum majus. Immunolocalization analysis using anti-T7 antibodies showed nucleolar localization of most of the T7 epitope-tagged NtSIP2 proteins. A similar analysis with the T7-tagged 6b protein also showed subnucleolar as well as nuclear localization of the 6b protein. These results suggest the involvement of 6b along with NtSIP2 in certain molecular processes in the nucleolus as well as the nucleoplasm.

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    • "Another 6b-interacting protein, NtSIP2, was found to be weakly homologous to the Ptta/En/Spm family of plant transposases (Kitakura et al. 2008). Although the biological significance of the observed similarity in the protein sequence is unclear, NtSIP2 localizes to nuclei, particularly to nucleoli, and can interact with both 6b and NtSIP1 in a yeast two-hybrid assay. "
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    • "f genes related to plant cell proliferation , and various hypotheses have been proposed to explain the effects of 6b on plant cell growth . The repeating Glu residue loop ( residues 164 – 184 ) was reported to interact with NtSIP1 , which contains the trihelix motif ( Kitakura et al . 2002 ) , and NtSIP2 , which is homologous to the TNP1 protein ( Kitakura et al . 2008 ) . However , the 6bDA mutant protein ( lacking the repeating Glu residue loop 164 – 184 ) retains the ability to interact with Arabi - dopsis histone H3 , SE , and AGO1 ( Terakura et al . 2007 ; this study ) . It appears that there are two groups of proteins interacting with 6b : one group targeting this acidic loop , and the other gro"
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