Fig. 1. Disease-linked point mutations of human lamins A and C expressed in HeLa cells. (A) Organization of the lamin A and C polypeptides. Both lamins share identical sequence from residues 1 to 566. The location of each point mutation is indicated in the diagram. The black bar within the lamin A and C nonhelical C-terminal domains marks the position of the nuclear localization sequence. The immunoblots in (B) demonstrate that HA-tagged wild-type and mutant lamin cDNAs encode proteins of the appropriate molecular weight. The various lamin A alleles (HA-LaA) appear as a doublet, with the lower band corresponding to mature lamin A. The upper band most likely corresponds to lamin A₀, which has yet to undergo C-terminal proteolytic processing. This processing event appears slightly retarded in LaA L85R where the A₀:A ratio is approximately 1.6:1. All of the other lamin A alleles exhibit an A₀:A ratio of 1:1. The various lamin C alleles (HA-LaC) have identical mobilities.