TdT interacting factor 1 enhances TdT ubiquitylation through recruitment of BPOZ-2 into nucleus from cytoplasm.

We isolated human cDNA clone encoding Bood POZ containing gene type 2 (BPOZ-2) as a gene with a product that binds to TdT interacting factor 1 (TdIF1) using a yeast two-hybrid system. BPOZ-2 is an adaptor for E3 ligase CUL3 and participates in developmental processes. The binding between BPOZ-2 and TdIF1 was confirmed by GST pull-down and immunoprecipitation assays using specific antibodies against BPOZ-2 and TdIF1 in vitro and in vivo. Although when BPOZ-2 solely was expressed in COS7 cells, BPOZ-2 was observed mainly within the cytoplasm, co-transfection of pEGFP-BPOZ-2 and pDsRed-TdIF1 into COS7 cells resulted in co-localization of EGFP-BPOZ-2 and DsRed-TdIF1 within the nucleus. TdIF1 may recruit BPOZ-2 into the nucleus from the cytoplasm by directly binding to BPOZ-2. BPOZ-2 enhanced TdT ubiquitylation when TdIF1 was expressed together with BPOZ-2 in 293T cells, strongly suggesting that the recruitment of BPOZ-2 into the nucleus from the cytoplasm is significant for the TdT ubiquitylation within the nucleus.