Figure 3.

BrdU is incorporated into chromosomal DNA during S phase. (A) Small unbudded TK⁺ yeast cells (E1000) were isolated by centrifugal elutriation and incubated at 25°C in the presence of either 400 µg/ml BrdU or 20 µCi/ml [³H]uracil. α-Factor was added to the cultures at 150 min to prevent a second round of DNA replication. Samples were collected every 15 min and incorporation of BrdU and ³H into DNA was measured as described in Materials and Methods. ³H c.p.m. values (25 × 10³ at 100%) are the means ± SD of three independent cell samples. (B) Cell cycle progression in the presence of BrdU was monitored by FACS analysis and was indistinguishable from cells grown without BrdU (data not shown).