J. Biol. Chem., Vol. 259, Issue 5, 2693-2696, Mar, 1984
Lamin B from rat liver nuclei exists both as a lamina protein and as an intrinsic membrane protein
S Lebel and Y Raymond
Rat liver nuclear matrix structures were isolated while preserving the
integrity of the nuclear envelope, i.e. in the absence of any detergent
extraction. In order to determine the relationships between the nuclear
membranes and peripheral lamina, nuclear matrix-envelope preparations were
submitted to sodium carbonate extraction (0.1 M, pH 11.5), a solvent which
solubilizes both peripheral membrane proteins and membrane-enclosed
contents. One-dimensional and two-dimensional sodium dodecyl
sulfate-polyacrylamide gel electrophoresis analysis of material insoluble
in sodium carbonate confirmed that intrinsic membrane proteins were indeed
retained in the membrane structures. Approximately 50 to 60% of the lamin B
present in matrix-envelope preparations was found in these insoluble
membranes while a smaller amount of lamin A and even less of lamin C
resisted complete extraction. The identity of the lamins was confirmed by
their migration on two-dimensional gels and by comparison of
one-dimensional peptide maps. The same results were obtained using nuclear
membranes prepared by a milder heparin procedure. The location of lamin B
as an intrinsic membrane protein was also established by photoaffinity
labeling with the membrane- penetrating reagent azidopyrene. A small but
reproducible amount of labeling occurred as well on lamin A polypeptides.
These results support the hypothesis that the peripheral lamina is attached
to the nuclear envelope and anchored there via the presence of lamin B
molecules within the bilayer of the inner nuclear membrane.
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