Binding of heterochromatin protein 1 to the nuclear envelope is regulated by a soluble form of tubulin.
We have previously shown that the mouse heterochromatin protein 1 homologue M31 interacts dynamically with the nuclear envelope. Using quantitative in vitro assays, we now demonstrate that this interaction is potently inhibited by soluble factors present in mitotic and interphase cytosol. As indicated by depletion and order-of-addition experiments, the inhibitory activity co-isolates with a 55-kDa protein, which binds avidly to the nuclear envelope and presumably blocks M31-binding sites. Purification of this protein and microsequencing of tryptic peptides identify it as alpha2/6:beta2-tubulin. Consistent with this observation, bona fide tubulin, isolated from rat brain and maintained in a nonpolymerized state, abolishes binding of M31 to the nuclear envelope and aborts M31-mediated nuclear envelope reassembly in an in vitro system. These observations provide a new example of "moonlighting," a process whereby multimeric proteins switch function when their aggregation state or localization is altered.
Department of Basic Sciences, University of Crete School of Medicine, 71 110 Heraklion, Crete, Greece.
N
N
Kourmouli
G
G
Dialynas
C
C
Petraki
A
A
Pyrpasopoulou
P B
PB
Singh
S D
SD
Georgatos
P A
PA
Theodoropoulos
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000378:metabolism*; D016889:Endometrial Neoplasms; D005260:Female; D006367:HeLa Cells; D006570:Heterochromatin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009685:Nuclear Envelope / Q000502:physiology* / Q000648:ultrastructure; D010446:Peptide Fragments / Q000737:chemistry; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
C096188:Cbx1 protein, mouse; D002868:Chromosomal Proteins, Non-Histone; D006570:Heterochromatin; D010446:Peptide Fragments; D011994:Recombinant Proteins; D014404:Tubulin; D000090266:Chromobox Protein Homolog 5