Figure 2.

Carboxy-terminal processing of lamins. The flow diagram illustrates the sequential processing steps necessary to convert prelamin A, prelamin B1, and prelamin B2 to mature proteins. Each successive step requires the completion of the previous modification. Lamins B1 and B2 do not undergo the final protease cleavage step and remain permanently farnesylated and carboxymethylated. The fate of the 15-amino-acid farnesylated peptide removed from prelamin A is unknown, but the peptide is thought to be degraded.