The thr attenuator is a DNA element containing a G+C-rich dyadsymmetry followed by a run of poly(dT), and is reported to be a rho-independentterminator. The effects of the concentrations of nucleoside triphosphates onthe transcription of bacteriophage T7 polymerases were analyzed at the thrattenuator in the supercoiled and linearized DNA templates. T7 RNA polymeraseshowed high termination efficiency in the low concentration of nucleosidetriphosphates at the thr attenuator in the both linearized and supercoiledtemplates. The thr attenuator inthe supercoiled DNA template always causedmore T7 RNA polymerase to cease transcription than that in the linearized DNAtemplate. Also, when the concentration of ATP is limited from 5 uM to 150 uM,the transcript production by T7 RNA polymerase was at least two folds morethan that in the limited supply of any other nucleoside triphosphates. Thisindicates that ATP may compete with GTP in affecting transcription of T7 RNApolymerase.

　　　　　在DNA模板上，thr attenuator是一個含GC逆對稱尾一串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thrattenuator為測試模式，來分析和比較噬菌體T7 RNA聚合?t，在不同的核??酸濃度之下的轉錄反應。結果顯示，在低濃度的核??酸下，thr attenuator 無論在線性狀和超螺旋狀DNA載體，都能阻止較多的噬菌體T7聚合?t進行轉錄，而與線性狀DNA載體比較，噬菌體T7RNA聚合?t在超螺旋狀DNA載體的thr attenuator上，顯示出較高的較錄終止現像。此外，在ATP的濃度限制在5uM到150uM之間時，T7 RNA聚合?t所產生的轉錄產物，較其在其它核??酸下所產的轉錄產物，多出至少兩倍，這表示ATP可能和GTP競爭於影響T7 RNA聚合?t的轉錄。