Centromere

The centromere is the part of a chromosome that links sister chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore. Centromeres were first defined as genetic loci that direct the behaviour of chromosomes. Their physical role is to act as the site of assembly of the kinetochore - a highly complex multiprotein structure that is responsible for the actual events of chromosome segregation - e.g. binding microtubules and signalling to the cell cycle machinery when all chromosomes have adopted correct attachments to the spindle, so that it is safe for cell division to proceed to completion (i.e. for cells to enter anaphase). There are broadly speaking two types of centromeres. "Point centromeres" bind to specific proteins that recognise particular DNA sequences with high efficiency. Any piece of DNA with the point centromere DNA sequence on it will typically form a centomere if present in the appropriate species. The best characterised point centromeres are those of the budding yeast, Saccharomyces cerevisiae. "Regional centromeres" is the term coined to describe most centromeres, which typically form on regions of preferred DNA sequence, but which can form on other DNA sequences as well. The signal for formation of a regional centromere appears to be epigenetic. Most organisms, ranging from the fission yeast Schizosaccharomyces pombe to humans, have regional centromeres.