Distribution of gamma satellite DNA on the human X and Y chromosomes suggests that it is not required for mitotic centromere function

The bulk of the DNA found at human centromeres is composed of tandemly arra nged repeats, the most abundant of which is alpha satellite. Other human ce ntromeric repetitive families have been identified, one of the more recent being gamma satellite. To date, gamma satellite DNAs have been reported at the centromeres of human chromosomes 8 and X. Here, we show that gamma-X sa tellite DNA is not interspersed with the major DZX1 alpha-X block, but rath er is organised as a single array of approximately 40-50 kb on the short-ar m side of the alpha satellite domain. This repeat array is absent on two mi totically stable Xq isochromosomes. Furthermore, a related repeat DNA has b een identified on the human Y chromosome. Fluorescence in situ hybridisatio n has localised this satellite DNA to the long arm side of the major DYZ3 a lpha-Y domain, outside the region previously defined as that required for m itotic centromere function. Together, these data suggest that while blocks of highly related gamma satellite DNAs are present in the pericentromeric r egions of both human sex chromosomes, this repeated DNA is not required for mitotic centromere function.