Chromatin and Chromosomes, the Role and Function of SMC Proteins

Abstract

Packing genomic DNA into the eukaryotic cell nucleus is a task similar to stowing the London Underground network in a suitcase. Centimetres of DNA are compacted into micrometre-sized, rod-shaped chromosomes. This allows genetic material to be made small enough for faithful segregation to opposite cell halves, and compact enough to withstand the forces generated during this process. Over the past two decades, members of the evolutionarily ancient ‘Structural Maintenance of Chromosomes (SMC)’ family of protein complexes have emerged as principal structural chromosome components. I will discuss the mechanism of how these ring-shaped protein complexes encircle DNA, helped by a loading factor whose mutation causes severe human developmental disorders. I will also discuss how SMC complexes bind not only one, but two DNAs, a likely prerequisite for their many roles in chromosome biology. Finally, we will consider models of how SMC complexes might achieve the enormous DNA packaging task, working towards an image of what the inside of a chromosome might look like.