Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
HP1-type chromodomain proteins self-associate as well as interact with the inner nuclear membrane protein LBR (lamin B receptor) and transcriptional coactivators TIF1alpha and TIF1beta. The domains of these proteins that mediate their various interactions have not been entirely defined. HP1-type proteins are predicted by hydrophobic cluster analysis to consist of two homologous but distinct globular domains, corresponding to the chromodomain and chromo shadow domain, separated by a hinge region. We show here that the chromo shadow domain mediates the self-associations of HP1-type proteins and is also necessary for binding to LBR both in vitro and in the yeast two-hybrid assay. Hydrophobic cluster analysis also predicts that the nucleoplasmic amino-terminal portion of LBR contains two globular domains separated by a hinge region. The interactions of the LBR domains with an HP1-type protein were also analyzed by the yeast two-hybrid and in vitro binding assays, which showed that a portion of the second globular domain is necessary for binding. The modular domain organization of HP1-type proteins and LBR can explain some of the diverse protein-protein interactions at the chromatin-lamina-membrane interface of the nuclear envelope.