Heterotypic and homotypic associations between the nuclear lamins: site-specificity and control by phosphorylation.
Using purified components in affinity chromatography and blot binding assays, we have found that rat liver lamins A, B, and C can associate in homotypic and heterotypic fashions. Heterotypic A-B and C-B complexes are unusually stable and involve the common amino-terminal domain of lamins A and C, but not their helical "rod" domain. A synthetic peptide, comprising the first 32 amino acid residues of lamins A and C, is able to fully compete with the intact molecules for binding to lamin B. Conversely, heterotypic A-C associations and homotypic A-A and C-C interactions appear significantly weaker than A/C-B binding and do not involve the lamin A and C amino-terminal domain. Homotypic B-B complexes are not formed to any considerable extent unless isolated lamin B subunits are "superphosphorylated" in vitro with protein kinase A. However, when lamins A and C are similarly modified, no changes in their binding specificity can be detected. These data suggest that the nuclear lamina, unlike other multicomponent intermediate filaments, constitutes a nonobligatory heteropolymer. They also indicate that cAMP-dependent phosphorylation of interphase lamin B could cause remodeling of the lamina and establishment of homopolymeric domains.
Georgatos
S D
SD
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021.
Stournaras
C
C
Blobel
G
G
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D007457:Iodine Radioisotopes; D034904:Lamin Type A; D034921:Lamin Type B; D034882:Lamins; D008099:Liver / Q000378:metabolism; D046911:Macromolecular Substances; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D051381:Rats
D007457:Iodine Radioisotopes; D034904:Lamin Type A; D034921:Lamin Type B; D034882:Lamins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D010761:Phosphorus Radioisotopes; D000255:Adenosine Triphosphate