Fig. 6. The distribution of Cyclin A and Cyclin B in Cdc16^RNAi and Cdc27^RNAi cells. (A) The distribution of Cyclin A (blue in merged image; shown alone in black and white), DNA (red) and microtubules (green). In mock-treated cells, Cyclin A stains the condensing mitotic chromatin in prophase cells (panel 1) but is not detectable on the chromosomes by metaphase when the chromosomes are usually visible as a `shadowed' region in the cyclin A channel; arrow, panel 2). This is also true of Cdc16<sup>RNAi</sup> cells (panel 3) but is not true of Cdc27<sup>RNAi</sup> cells where Cyclin A sometimes strongly stains metaphase chromosomes (panel 4), and the DNA `shadow' normally seen in the cyclin A channel is usually not detectable (panel 5). (B) The distribution of Cyclin B (blue in merged image or shown alone in black and white), DNA and microtubules (colours as in A). In mock-treated cells, Cyclin B stains centrosomes in prophase (arrows, panel 1) and centrosomes and spindles in some metaphase cells (panel 2) but not others (panel 3). We failed to detect Cyclin B on centrosomes or spindles in any mock-treated cells in anaphase (panel 4). In Cdc16^RNAi or Cdc27^RNAi cells, Cyclin B behaved in a similar manner to mock-treated cells, but it was very occasionally detectable on centrosomes and spindles in anaphase-like cells, particularly in Cdc27^RNAi-treated cells (panel 5), suggesting that cyclin B is not being degraded properly in at least some of these cells. Bar, 5 µm.