From bacteria to humans, all forms of life are based on the capacity of one cell to divide into two or more identical daughter cells. In doing so, cells have to produce a copy of their genetic material (DNA) and separate it into two identical sets, one for each daughter cell. Immediately after duplication and before its segregation, DNA is packed in chromosomes that consist of two identical strands joined at a point along their length, called centromeres. Centromeres ensure accurate separation of the chromosomes between daughter cells by directing the assembly of the molecular scaffolding that helps separate cells. The group of scientists led by the IBMB-CSIC Professor and IRB Barcelona researcher Ferran Azorn has identified the main instrument that Drosophila cells use to control the levels of the CenH3 protein, a key element for defining the identity and function of the centromere in the fruit fly.
CenH3 is a unique variant of conventional histones proteins responsible for DNA packaging found exclusively in the centromeres of all eukaryotes studied to date. "The presence of CenH3 in chromosome regions other than the centromere is sufficient to cause defects in chromosome separation in Drosophila and in budding yeast", explains Azorn. In yeast and Drosophila, the controlled degradation of CenH3 is known to be one of the mechanisms that regulate its location in the centromere. How this mechanism works, however, has been a mystery until now. The study, led by Azorn and published online on August 25 in Current Biology, shows that CenH3 interacts specifically with the protein partner of pair (Ppa), involved in directing proteins toward degradation. "We have demonstrated that degradation of CenH3 is essential for limiting its presence at the centromeres and that this degradation is mediated by the protein Ppa, which targets CenH3 to one of the cell's degradation mechanisms, the proteasome", explains Azorn. The proteasome is a b
|Contact: Itziar Castanedo|
Institute for Research in Biomedicine (IRB Barcelona)