• Chen T, Muratore TL, Schaner-Tooley CE, Shabanowitz J, Hunt DF, Macara IG. N-terminal alpha-methylation of RCC1 is necessary for stable chromatin association and normal mitosis. Nature cell biology. 2007 May;9(5). 596-603. PMID: 17435751 [PubMed].

Abstract 

Regulator of chromatin condensation 1 (RCC1) is the only known guanine nucleotide-exchange factor for the Ran GTPase and has pivotal roles in nucleo-cytoplasmic transport, mitosis, and nuclear-envelope assembly. RCC1 associates dynamically with chromatin through binding to histones H2A and/or H2B in a Ran-regulated manner. Here, we report that, unexpectedly, the amino-terminal serine or proline residue of RCC1 is uniquely methylated on its alpha-amino group. Methylation requires removal of the initiating methionine, and the presence of proline and lysine at positions 3 and 4, respectively. Methylation-defective mutants of RCC1 bind less effectively than wild-type protein to chromatin during mitosis, which causes spindle-pole defects. We propose a bimodal attachment mechanism for RCC1 in which the tail promotes stable RCC1 association with chromatin through DNA binding in an alpha-N-methylation-dependent manner. These data provide the first known function for N-terminal protein methylation.