Detection of HP1α on D17Z1-based artificial chromosomes. (a-d) Cell lines stably expressing a Myc-tagged form of HP1α. HP1α was detected using an anti-Myc antibody (red). The artificial chromosomes (about 1-3 Mb; indicated by small arrows) in lines (a) 17-D34-1.A2 and (b) 17-E29-1.C23 exhibit faint HP1α staining at a level similar to the general arm staining. Larger artificial chromosomes (3-10 Mb; small arrow) in lines (c) 17-C20-1.B22 and (d) 17-B12-1.B10 stain strongly for HP1α. Inserts in (a-c) show either DAPI (blue)-stained artificial chromosomes or HP1α (red). Host 17 centromere regions are indicated by the large arrows in (a-c). In (d), simultaneous staining for CENP-A (green) shows that CENP-A is restricted to a portion of the artificial chromosome (arrows) whereas the HP1α signal coats the entire artificial chromosome. In contrast to CENP-A, which is present at comparable levels on all artificial chromosomes tested [12,13,58] and host kinetochores , HP1α staining levels are more variable at host centromere regions (d).