噬菌體RNA聚合酵素在不同濃度的鹽類和核甘酸之下的轉錄終止反應

Effects of the Concentration of Nucleoside Triphosphates on the Transcription of Bacteriophage T7 RNA Polymerase in the Linearized and Supercoiled DNA Templates

在DNA模板上，thr attenuator是一個含GC逆對稱尾隨一串T的構造，也是一個rho-independent的終結子。在此報告中，以在線性狀和超螺旋狀DNA載體中的thr attenuator為測試模式，來分析和比較噬菌體T7 RNA聚合酶，在不同的核苷酸濃度之下的轉錄反應。結果顯示，在低濃度的核苷酸下，thr attenuator無論在線性狀和超螺旋狀DNA載體中，都能阻止較多的噬菌體T7聚合酶進行轉錄，而與線性狀DNA載體比較，噬菌體T7 RNA聚合酶在超螺旋狀DNA載體的thr attenuator上，顯示出較高的轉錄終止現像。此外，在ATP的濃度限制在5µm到150µm之間時，T7 RNA聚合酶所產生的轉錄產物，較其在其它核苷酸下所產生的轉錄產物，多出至少兩倍，這表示ATP可能和GTP競爭於影響T7 RNA聚合酶的轉錄。

The thr attenuator is a DNA clement containing a G+C-rich dyad symmetry followed by a run of poly(dT), and is reported to be a rho-independent terminator. The effects of the concentrations of nucleoside triphosphates on the transcription of bacteriophage T7 polymerases were analyzed at the thr attenuator in the supercoiled and linearized DNA templates. T7 RNA polymerase showed high termination efficiency in the low concentration of nucleoside triphosphates at the thr attenuator in the both linearized and supercoiled templates. The thr attenuator in the supercoiled DNA template always caused more T7 RNA polymerase to cease transcription than that in the linearized DNA template. Also, when the concentration of ATP is limited from 5 µm to 150 µm, the transcript production by T7 RNA polymerase was at least two folds more than that m the limited supply of any other nucleoside triphosphates. This indicates that ATP may compete with GTP in affecting transcription of T7 RNA polymerase.