Approximately 70% of the late erythroid progenitor cells (E-CFU) which are present in normal bone marrow are killed by exposure to high specific activity tritiated thymidine (3H-TdR) in vitro or to hydroxyurea in vivo, indicating that a high proportion of these cells synthesize DNA. Their cell cycle was further analyzed by sedimentation at unit gravity. The modal sedimentation rate of 7.4 mm/h appeared to correspond to the fraction that is killed by 3H-TdR. Cells sedimenting at 6.0 and 9.5 mm/h were not susceptible to kill by 3H-TdR and correspond to cells in, respectively, G1 and G2/M. Based on a buoyant density of 1.077 g/cm3, the modal diameter of cells in G1 was calculated to be 8.3 micron, in S 9.2 micron and in G2/M 10.5 micron. The E-CFU population appeared to be composed of about 18% G1 cells, about 70% S phase cells and about 12% G2/M cells. The surviving fraction of E-CFU 2 h after intraperitoneal administration of 1 g/kg hydroxyurea was identified as being mainly a synchronous population in early S phase. The data are best explained by a short duration of G1 and G2/M phases.

中文翻译：

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通过单位重力沉降分析晚期红系祖细胞的细胞周期。

正常骨髓中大约70％的晚期红系祖细胞（E-CFU）通过体外或体内暴露于高比活性tri化胸苷（3H-TdR）或体内羟基脲的杀死，这表明这些细胞合成DNA。通过在单位重力下的沉降进一步分析了它们的细胞周期。7.4 mm / h的模式沉积速率似乎对应于被3H-TdR杀死的部分。沉降速度为6.0和9.5 mm / h的细胞不易被3H-TdR杀死，并且分别对应于G1和G2 / M中的细胞。基于1.077 g / cm3的浮力密度，G1中细胞的众数直径计算为8.3微米，S 9.2微米和G2 / M 10.5微米。E-CFU群体似乎由约18％的G1细胞组成，大约70％的S期细胞和大约12％的G2 / M细胞。腹腔注射1 g / kg羟基脲后2 h E-CFU的存活分数被确定为主要是S期早期的同步种群。最好通过G1和G2 / M阶段的较短持续时间来解释数据。