Taylor J H, Hozier J C
Chromosoma. 1976 Sep 24;57(4):341-50. doi: 10.1007/BF00332159.
CHO cells in culture were synchronized by mitotic selection, allowed to reattach to plastic flasks, and reach S phase in the presence of fluorode-oxyuridine at concentrations known to completely block the synthesis of thymidylate. The cells were released from the block with 3H-thymidine for pulses of 4, 8, 12, 24 and 40 min and DNA fiber autoradiographs prepared. An analysis of the spacing between origins of replication indicates that sites are available at intervals of about 4 mum along most of the DNA. Chain growth proceeds at about 1,000 nucleotides per minute and some of the closely situated sites become continuous, labeled segments after 8-12 min. However, unlabeled segments are still present between the replicated segments after 40 min. The data may be interpreted as evidence for regularly spaced initiation sites which are available in CHO cells, even though only one in 10-15 of these may be utilized for initiation each cycle under normal growth conditions in these cultures.
培养中的中国仓鼠卵巢（CHO）细胞通过有丝分裂选择同步化，使其重新附着于塑料培养瓶，并在已知能完全阻断胸苷酸合成的氟脱氧尿苷存在下进入S期。用³H - 胸腺嘧啶核苷对细胞进行4、8、12、24和40分钟的脉冲处理以解除阻断，并制备DNA纤维放射自显影片。对复制起点之间间距的分析表明，沿着大部分DNA，每隔约4μm就有可用的位点。链生长速度约为每分钟1000个核苷酸，一些紧密相邻的位点在8 - 12分钟后成为连续的标记片段。然而，40分钟后，复制片段之间仍存在未标记的片段。这些数据可以解释为CHO细胞中存在规则间隔的起始位点的证据，尽管在这些培养物的正常生长条件下，每个周期中这些位点中只有1/10 - 1/15可用于起始复制。
