Evolvement of LEM-proteins as chromatin tethers at the nuclear periphery

摘要

The nuclear envelope in eukaryotic cells has important roles in chromatin organization. The inner nuclear membrane contains over 60 transmembrane proteins. LAP2-emerin-MAN1 (LEM)-domain containing proteins of the inner nuclear membrane are involved in tethering chromatin to the nuclear envelope and affect gene expression. They contain a common structural, bi-helical motif, the so-called LEM domain, which mediates binding to a conserved chromatin protein, Barrier-to-Autointegration Factor (BAF). Interestingly, this domain is highly related to other bi-helical motifs, termed helix-extension-helix (HeH) - and SAF-Acinus-PIAS (SAP) motifs, which are directly linked to DNA. Here we summarize evidence that the LEM motif evolved from the HeH and SAP domains concomitantly with BAF. In addition we discuss the potential evolution of HeH/SAP and LEM domain containing proteins and their role in chromatin tethering and gene regulation from unicellular eukaryotes to mammals.