Roles of LAP2 proteins in nuclear assembly and DNA replication: truncated LAP2beta proteins alter lamina assembly, envelope formation, nuclear size, and DNA replication efficiency in Xenopus laevis extracts

• Published in: The Journal of cell biology 1999-03, Vol.144 (6), p.1083-1096
• Main Authors: Gant, T M, Harris, C A, Wilson, K L
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Binding Sites; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cell Nucleus - ultrastructure; Cell-Free System; Cellular biology; Chromatin - metabolism; Cloning, Molecular; Deoxyribonucleic acid; DNA; DNA Primers - genetics; DNA Replication - drug effects; DNA Replication - physiology; DNA, Complementary - genetics; DNA-Binding Proteins; Female; Humans; In Vitro Techniques; Lamins; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Microscopy, Electron; Molecular Sequence Data; Nuclear Envelope - metabolism; Nuclear Proteins - chemistry; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Oocytes - drug effects; Oocytes - metabolism; Oocytes - ultrastructure; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Peptide Fragments - pharmacology; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Recombinant Proteins - pharmacology; Sequence Homology, Amino Acid; Xenopus laevis
• ISSN: 0021-9525; 1540-8140

Humans express three major splicing isoforms of LAP2, a lamin- and chromatin-binding nuclear protein. LAP2beta and gamma are integral membrane proteins, whereas alpha is intranuclear. When truncated recombinant human LAP2beta proteins were added to cell-free Xenopus laevis nuclear assembly reactions at high concentrations, a domain common to all LAP2 isoforms (residues 1-187) inhibited membrane binding to chromatin, whereas the chromatin- and lamin-binding region (residues 1-408) inhibited chromatin expansion. At lower concentrations of the common domain, membranes attached to chromatin with a unique scalloped morphology, but these nuclei neither accumulated lamins nor replicated. At lower concentrations of the chromatin- and lamin-binding region, nuclear envelopes and lamins assembled, but nuclei failed to enlarge and replicated on average 2. 5-fold better than controls. This enhancement was not due to rereplication, as shown by density substitution experiments, suggesting the hypothesis that LAP2beta is a downstream effector of lamina assembly in promoting replication competence. Overall, our findings suggest that LAP2 proteins mediate membrane-chromatin attachment and lamina assembly, and may promote replication by influencing chromatin structure.