The organization and function of chromosomes

Abstract

The EMBO Workshop on Chromosome Structural Elements was held in the Villa Mondragone, south of Rome, Italy, between 29 September and 3 October 2005, and was organized by F. Ascenzioni, S. Bacchetti, G. Novelli and M. Savino. ![][1] At the end of the summer of 2005, around 60 scientists came together in Rome to discuss various aspects of eukaryotic chromosome biology, including telomeres, centromeres, origins of replication, genome evolution and nuclear organization. Each of these topics is a well‐established field with its own specialist meetings and, for the workshop's participants, this was an unusual and welcome opportunity to hear talks outside their own speciality: the centromere and telomere fields rarely meet! In this report, we consider just a few of the broad range of topics discussed. In its opening session, the meeting focused on the telomere. In most eukaryotes studied (the notable exception being Drosophila and other dipterans), telomeres are composed of tandem, simple, G‐rich repeats. Telomeres have two key functions. First, the complex of proteins that nucleates on the telomeric DNA maintains its structural stability and ensures that the natural end is distinguished from a double‐strand break. Second, they provide a mechanism, which operates in immortal cells, to compensate for the progressive loss of DNA from the chromosome end that occurs as a result of ‘conventional’ DNA replication processes. The most common ‘top‐up’ mechanism involves the ribonucleoprotein complex, telomerase, which synthesizes telomere repeats de novo at the terminus. Data were presented on telomeric DNA structure, the regulation of telomerase activity, and on non‐telomeric roles for some proteins that were thought, until recently, to be telomere‐specific. It has been known since 1989 that G‐rich telomeric DNA from ciliates can form G‐quadruplex structures (G4) in vitro , a process facilitated by the telomere‐end‐binding protein TEBP‐β. Evidence that such structures could form in … [1]: /embed/graphic-1.gif