Brawerman G, Diez J
Cell. 1975 Jul;5(3):271-80. doi: 10.1016/0092-8674(75)90102-6.
The poly(A) sequences at the 3' end of mRNA and nuclear RNA molecules of mouse sarcoma and Chinese hamster cells are subject to an elongation process distinct from de novo synthesis. This process continues in cells treated with a high level of actinomycin D to block transcription. This results in the labeling of the steady-state poly(A) population in the cytoplasm and of unusually long poly(A) segments in the nucleus. In cells incubated with 3H-adenosine in the absence of drug treatment, cytoplasmic steady-state poly(A) segments with short labeled sequences at the 3' end can be detected by their heterogenous size distribution and by measurements of adenosine and AMP released by alkaline hydrolysis. These measurements indicate an average size of 8 residues for the labeled sequences. In the nucleus, a slow elongation of preexisting poly(A) chains can also be detected through measurements of AMP and adenosine. The cytoplasmic elongation process leads to turnover of the 3' end of the poly(A) sequence on mRNA, because of concomitant removal of AMP residues. It is apparently not linked to mRNA translation. The Chinese hamster and mouse sarcoma cells appear to differ markedly with respect to relative extents of poly(A) chain extension and de novo synthesis.
小鼠肉瘤和中国仓鼠细胞的mRNA及核RNA分子3'端的多聚腺苷酸（poly(A)）序列会经历一个与从头合成不同的延伸过程。在用高浓度放线菌素D处理以阻断转录的细胞中，这一过程仍会继续。这导致细胞质中稳态多聚腺苷酸群体以及细胞核中异常长的多聚腺苷酸片段被标记。在未进行药物处理的情况下用3H-腺苷孵育的细胞中，通过其异质大小分布以及对碱性水解释放的腺苷和AMP的测量，可以检测到3'端带有短标记序列的细胞质稳态多聚腺苷酸片段。这些测量表明标记序列的平均大小为8个残基。在细胞核中，通过对AMP和腺苷的测量也能检测到已有多聚腺苷酸链的缓慢延伸。由于伴随AMP残基的去除，细胞质延伸过程导致mRNA上多聚腺苷酸序列3'端的周转。它显然与mRNA翻译无关。中国仓鼠细胞和小鼠肉瘤细胞在多聚腺苷酸链延伸和从头合成的相对程度方面似乎有显著差异。
