We have examined the nuclear localization of isoprenylated proteins in CHO-K1 cells labeled with [14C]mevalonate. Nuclear proteins of 68, 70, and 74 kD, posttranslationally modified by an isoprenoid, are also components of a nuclear matrix-intermediate filament preparation from CHO cells. Furthermore, the 68-, 70-, and 74-kD isoprenylated polypeptides are immunoprecipitated from cell extracts with two different anti-lamin antisera. Based on exact two-dimensional comigration with lamin B, both from rat liver lamin and CHO nuclear matrix-intermediate filament preparations, and its immunoprecipitation with anti-lamin antisera, we conclude that the 68-kD isoprenylated protein found in nuclei from [14C]mevalonate-labeled CHO cells is lamin B. The more basic 74-kD isoprenylated nuclear protein is similar in molecular mass and isoelectric pH variants to the lamin A precursor polypeptide reported by others. Starving cells for mevalonate results in a dramatic accumulation of a polypeptide that comigrates on two-dimensional, non-equilibrium pH gradient electrophoresis (NEPHGE) gels with the 74-kD isoprenylated protein. The 70-kD isoprenylated protein, which is resolved on NEPHGE gels as being higher in molecular mass and slightly more basic than lamin B, has not yet been identified.

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