| Abstract: | Rat embryo cell cultures were synchronized by a double thymidine block. The DNA replication phase (S) was divided into an early, middle, and late period. Cell cultures in the early, middle, or late S phase were pulsed with 0.1 muM 5-bromo(3)H]deoxyuridine (BrdU) or equimolar (3)H]dT. DNA-DNA reassociation experiments of each sample revealed that (3)H]BrdU was more concentrated in the intermediate repetitive than the repetitive or unique DNA sequences of the early and middle S phase. In contrast, (3)H]dT was nearly uniformly jistributed throughout all nucleotide sequences during the entire S phase. synchronized rat cells were pulsed during various portions of the S phase with unlabeled 0.1 mM or 0.1 muM BrdU and examined for sytoplasmic immumofluorescence against the 30,000 molecular weight group-specific antigen (p30) of Friend mouse leukemia virus. Equally strong fluorescence was detected 12 hr later in cells treated with each concentration of BrdU. Furthermore, incorporation of BrdU during late S phase was suffieient to elicit maximal antigen expression. |
