INTEGRAL MEMBRANE-PROTEINS OF THE NUCLEAR-ENVELOPE INTERACT WITH LAMINS AND CHROMOSOMES, AND BINDING IS MODULATED BY MITOTIC PHOSPHORYLATION

Lamina-associated polypeptides (LAPs) 1A, 1B, 1C, and 2 are integral membrane proteins of the nuclear envelope associated with the nuclear lamina. Using in vitro assays, we show that LAPs 1A and 1B specifically bind to both lamins A and C and lamin B1, while LAP 2 associates only with lamin B1. LAP 2 also binds to mitotic chromosomes. The LAPs are phosphorylated during mitosis, and phosphorylation of LAP 2 by mitotic cytosol inhibits its binding to both lamin B1 and chromosomes. During late anaphase, LAP 2 associates with chromosomes prior to assembly of most lamins. Together, these data suggest that LAP 2 may have a key role in initial events of nuclear envelope reassembly, and that both LAP 2 and LAP 1 may be involved in attaching lamins to the nuclear envelope.