Kusamran T, Drake R, Wunderlich S M, Lau A, Baliga B S, Munro H N
Placenta. 1980 Apr-Jun;1(2):157-67. doi: 10.1016/s0143-4004(80)80024-5.
Human placentae obtained early in pregnancy or at full term were examined for RNA content per cell, RNA polymerase types and activities, and chromatin template availability. The RNA:DNA ratio fell from 0.7 at 15 to 20 weeks to 0.4 at 40 weeks of pregnancy. Since RNase activities were similar at both times, the reduction in RNA content was attributed not to increased degradation, but to reduced synthesis. At both stages of pregnancy, about 55 to 60 per cent of the RNA polymerase activity in isolated placental nuclei was accounted for by RNA polymerase II, as judged by suppression of activity with alpha-amanitin and by separation of the extracted polymerases on DEAE-Sephadex. The relative roles of changes in polymerase activity and template availability were measured in nuclei from 20- and 40-week placentae. Nuclei showed 20 per cent greater polymerase activity in full-term than in early placentae, but the template availability of isolated chromatin for transcription by RNA polymerase II was 70 per cent less at full term. We conclude that the reduced amount of RNA per cell in the full-term placenta is due to reduced template availability that more than offsets the slight increase in polymerase activity.
对妊娠早期或足月时获取的人胎盘进行了检查，以测定每个细胞的RNA含量、RNA聚合酶类型及活性，以及染色质模板的可用性。RNA与DNA的比率从妊娠15至20周时的0.7降至40周时的0.4。由于两个时期的核糖核酸酶活性相似，RNA含量的降低并非归因于降解增加，而是合成减少。在妊娠的两个阶段，通过α-鹅膏蕈碱抑制活性以及在二乙氨基乙基葡聚糖（DEAE-Sephadex）上分离提取的聚合酶判断，分离的胎盘细胞核中约55%至60%的RNA聚合酶活性由RNA聚合酶II引起。在来自20周和40周胎盘的细胞核中测定了聚合酶活性变化和模板可用性的相对作用。足月胎盘细胞核的聚合酶活性比早期胎盘高20%，但RNA聚合酶II转录时分离染色质的模板可用性在足月时少70%。我们得出结论，足月胎盘每个细胞中RNA量的减少是由于模板可用性降低，这超过了聚合酶活性的轻微增加。
