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Functional characterization of AtBPM1 protein in Arabidopsis thaliana

The BTB domain (also known as the POZ domain) is a versatile protein-protein interaction motif that participates in a wide range of cellular functions, including transcriptional regulation, cytoskeleton dynamics, ion channel assembly and gating, and targeting proteins for ubiquitination. BTB/POZ domain mediates homomeric dimerisation as well as interactions with a number of other proteins. It has been demonstrated for animals and plants that members of the BTB⁄POZ superfamily use their BTB⁄POZ domain to assemble with CUL3 protein, a scaffolding subunit of multimeric E3- ligases that polyubiquitinate their substrates and thereby target them for degradation via the 26S proteasome. MATH (Meprin and TRAF Homology) domain recognizes substrates that are going to be ubiquitinated is found amino-terminal to the BTB domain in MATH-BTB proteins. Although the role and target proteins of MATH-BTB proteins are not completely clear, their wide distribution and conservation indicate on important cellular functions. In Arabidopsis thaliana, the MATH-BTB (BPM) proteins comprise a small family of six members. Recently it is demonstrated that BPMs regulate ubiquitination of ethylene response factor/Apetala2 transcription factors via CUL3 and affect fatty acid metabolism in plants. Results of our investigations showed different predominant subcellular localizations of AtBPM1 and CUL3. AtBPM1 and CUL3 co-localize in cytoplasm, but in nucleus and especially in nucleolus where AtBPM1 was abundant co- localization with CUL3 is low. In addition, there was diverse cellular localization in different tissues of transgenic plants overexpressing AtBPM1, which suggest multiple roles of AtBPM1. Using tandem affinity purification, liquid chromatography and mass spectrometry, proteins from 13 days old seedlings of A. thaliana that interact with AtBPM1 were detected. Preliminary proteomic data suggest involvement of AtBPM1 in the oxidative stress and DNA methylation. We are currently engaged in determining the exact role of AtBPM1 in this important process.

BPM1; TAP tag; functional proteomics; DNA methylation; oxidative stress

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