Human protein MCM6 on HeLa cell chromatin

Minichromosome maintenance (Mcm) proteins perform essential functions regulating the replication of chromatin, Human cells, like other eukaryotic cells, express at least six Mcm proteins conserved in the central region, We have earlier described the primary structures of five human Mcm proteins, but the primary structure of the sixth human Mcm protein, MCM6, was identified only recently, We now use antibodies, specific for the MCM6 protein, to assess its intranuclear distribution, We find that a fraction of MCM6 protein occurs in the nucleosol, forming multiprotein complexes with other Mcm proteins, More importantly, we use for the first time micrococcal nuclease as a tool to investigate the association of MCM6 protein with chromatin, After short digestion times, a considerable fraction of the MCM6 protein is released from chromatin as a multiprotein complex that includes other Mcm proteins as well, In addition, fractions of MCM3 and MCM6 proteins are released by nuclease digestion as monomeric proteins indicating that at least these two Mcm proteins may also occur as single molecules on chromatin, The data also suggest that the chromatin regions with bound Mcm proteins are more vulnerable to nuclease attack than bulk chromatin and may therefore differ in the arrangement of nucleosomes.