Centromeres Take Flight: Alpha Satellite and the Quest for the Human Centromere

If It Looks like a Duck... There is ample evidence implicating a role for alpha satellite in centromere function. The first supportive evidence is " guilt by association " ; alpha satellite is the only known human DNA that is exclusively localized to the centromeric regions of all normal human chromosomes (Figure 1A). The arrays are composed of tandemly arranged 171 bp monomers organized into higher-order Chromosome inheritance must be amazingly efficient to ensure that each of the 100 trillion (10 14) cells in the repeats and range in size from 200 to 9000 kb (Figure 1B). Secondly, the human X and Y centromeres have been human body contains the full complement of 46 chromosomes required for normal viability and development. localized using chromosome rearrangements found in natural populations or created artificially by fragmenting Mitotic chromosome inheritance requires successful completion of three basic functions—replication, sister chromosomes with cloned telomeric DNA. In one study, two derivative chromosomes deleted for either most of chromatid cohesion and separation, and attachment to the Y long or short arms shared only 70 kb of overlapping and movement along the spindle. Chromosomes contain sequences that are predominantly composed of alpha many origins of DNA replication and sites of cohesion, satellite. All of the chromosome rearrangements ana-which helps to ensure that these tasks are accomplished lyzed to date retain at least 140 kb of alpha satellite, even when individual sites fail to function. However, in further implicating this sequence as having a role in many organisms spindle attachment occurs at a single, centromere function (Heller et al., 1996, and references localized region of each chromosome, the centromere therein). (Figure 1A), whose chromosome location does not ap-If guilt by association were sufficient, we would con-pear to change from one division to the next. What clude that alpha satellite is the " magic sequence " that specifies the site of centromere function, and how does determines human centromere identity and function, the centromere assemble the components necessary analogous to the conserved elements present in the S. for spindle attachment and movement? Despite the cerevisiae centromere. However, structural analyses are essential role of centromeres in cell division, answers currently not detailed enough to exclude the importance to these questions have baffled biologists for over a of nonalphoid DNA. Long-range restriction mapping century. The best-characterized centromere is found in the yeast Saccharomyces cerevisiae. In this unicellular eu-karyote, centromere function is conferred …