Prenylated prelamin A interacts with Narf, a novel nuclear protein

Prelamin A is farnesylated and methylated on the cysteine residue of a carb oxyl-terminal CaaX motif, In the nucleus, prelamin A is processed to lamin A by endoproteolytic removal of the final 18 amino acids, including the far nesylated cysteine residue, Using the yeast two-hybrid assay, we isolated a novel human protein, Narf, that binds the carboxyl-terminal tail of prelam in A. Narf has limited homology to iron-only bacterial hydrogenases and euk aryotic proteins of unknown function. Narf is encoded by a 2-kilobase mRNA expressed in all human cell lines and tissues examined. The protein is dete cted in the nuclear fraction of HeLa cell lysates on Western blots and can be extracted from nuclear envelopes with 0.5 M NaCl. When a FLAG epitope-ta gged Narf is expressed in HeLa cells, it is exclusively nuclear and partial ly co-localizes with the nuclear lamina, The farnesylation status of prelam in A determines its ability to bind to Narf. Inhibition of farnesyltransfer ase and mutation or deletion of the CaaX motif from the prelamin A tail dom ain inhibits Narf binding in yeast two-hybrid and in vitro binding assays. The prenyl-dependent binding of Narf to prelamin A is an important first st ep in understanding the functional significance of the lamin A precursor.