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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

SMC gene family

Reviewed February 2010

What are the SMC genes?

Genes in the structural maintenance of chromosomes (SMC) family provide instructions for making proteins that help regulate the structure and organization of chromosomes. Researchers have identified at least six SMC proteins, SMC1 through SMC6. (SMC1 usually refers to the protein made from either the SMC1A or the SMC1B gene.) SMC proteins have diverse functions within cells. In addition to organizing chromosomes, they are also involved in regulating the activity of genes, stabilizing cells' genetic information, and repairing damaged DNA.

SMC proteins interact with one another in pairs to form the core of several protein complexes. The most important of these complexes are cohesin and condensin.

Cohesin is made up of the SMC1 and SMC3 proteins, as well as two regulatory proteins. This protein complex helps control the activity of chromosomes during cell division. Before cells divide, they must copy all of their chromosomes. The copied DNA from each chromosome is arranged into two identical structures, called sister chromatids, which are attached to one another during the early stages of cell division. Cohesin holds the sister chromatids together.

Condensin is made up of the SMC2 and SMC4 proteins, along with three regulatory proteins. This protein complex helps determine the shape and structure of chromosomes during cell division. Within the nucleus, chromosomes are usually present as loose, tangled strands of DNA. However, when cells prepare to divide, the chromosomes are packed, or condensed, into tightly coiled structures. Condensin attaches to DNA to form these compacted chromosomes prior to cell division.

The SMC5 and SMC6 proteins also interact with one another, although less is known about their function. Studies suggest that they may form a protein complex that is involved in DNA repair.

Which genes are included in the SMC gene family?

The HUGO Gene Nomenclature Committee (HGNC) provides an index of gene families ( and their member genes.

Genetics Home Reference summarizes the normal function and health implications of these members of the SMC gene family: SMC1A and SMC3.

What conditions are related to genes in the SMC gene family?

Genetics Home Reference includes these conditions related to genes in the SMC gene family:

  • Cornelia de Lange syndrome

Where can I find additional information about the SMC gene family?

You may find the following resources about the SMC gene family helpful.

  • Molecular Biology of the Cell (fourth edition, 2002): Cohesins and Condensins Help Configure Replicated Chromosomes for Segregation ( (U.S. National Library of Medicine)

What glossary definitions help with understanding the SMC gene family?

cell ; cell division ; chromosome ; DNA ; DNA repair ; gene ; nucleus ; protein

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


These sources were used to develop the Genetics Home Reference summary for the SMC gene family.

  • Hirano T. At the heart of the chromosome: SMC proteins in action. Nat Rev Mol Cell Biol. 2006 May;7(5):311-22. Review. (
  • Losada A, Hirano T. Dynamic molecular linkers of the genome: the first decade of SMC proteins. Genes Dev. 2005 Jun 1;19(11):1269-87. Review. (
  • Jessberger R. The many functions of SMC proteins in chromosome dynamics. Nat Rev Mol Cell Biol. 2002 Oct;3(10):767-78. Review. (
  • Hirano T. The ABCs of SMC proteins: two-armed ATPases for chromosome condensation, cohesion, and repair. Genes Dev. 2002 Feb 15;16(4):399-414. Review. (
  • Harvey SH, Krien MJ, O'Connell MJ. Structural maintenance of chromosomes (SMC) proteins, a family of conserved ATPases. Genome Biol. 2002;3(2):REVIEWS3003. Epub 2002 Jan 30. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: February 2010
Published: November 23, 2015