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Oncogene. 1995 Dec 21;11(12):2689-97.

The BTB/POZ domain targets the LAZ3/BCL6 oncoprotein to nuclear dots and mediates homomerisation in vivo.

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U 124 INSERM, IRCL, Lille, France.


The LAZ3/BCL6 gene was identified by its disruption in 3q27 translocations associated with diffuse large cell lymphomas. It is predicted to be a transcription factor as it contains six Kr├╝ppel-like Zinc finger motifs and a N-terminal BTB/POZ domain, a protein/protein interaction interface that is widely conserved in Metazoans. Using two antisera raised against non overlapping regions of the predicted ORF, we demonstrate that the LAZ3/BCL6 protein appears as a close ca. 79 kDa doublet in B lymphoid cell lines with either a rearranged or a non rearranged LAZ3/BCL6 locus. By immunofluorescence experiments on transiently transfected COS-1 or NIH3T3 cells, we show that the LAZ3/BCL6 protein displays a punctuated nuclear localisation. This appears to rely on LAZ3/BCL6 proper folding and/or activities as it is impaired in a hormone reversible-fashion through fusion of LAZ3/BCL6 to the ligand-binding domain of the oestrogen receptor. Moreover, deletion of its BTB/POZ domain leads to the disappearance of the nuclear dots although the protein remains nuclear. In addition, by using the yeast two-hybrid system, we show that the LAZ3/BCL6 BTB/POZ domain homomerises in vivo. Thus, the LAZ3/BCL6 BTB/POZ domain has the capability to self-interact and target the protein to discrete nuclear substructures.

[Indexed for MEDLINE]

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