thr attenuator是在DNA模板上的一個富含GC逆對稱尾隨一串A的構造，也是一個rho-independent 的終結子。在此報告中，以thr attenuator為測試模式，去分析和比較噬菌T7、T3、和SP6 RNA聚合酵素，在不同濃度的鹽類、鎂離子、和核苷酸之下的轉錄反應。結果顯示，在低濃度鎂離子，或是高濃度鹽類之下，都能促進T7、T3、和SP6 RNA聚合酵素終止轉錄。並且在高濃度核苷酸之下，可增強T7和T3 RNA聚合酵素的終止反應，但是SP6 RNA聚合酵素則不受到影響。

The thr attenustor is a DNA element containing a G+C-rich dyad symmetry followed by a run of template poly (dA),and is reported to be a rho-independent terminator. The effects of the concentrations of salts,magnesium chloride,and nucleotide triphosphates on the transcription of bacteriophage T7,T3,and SP6 RNA polymerases were analyzed and compared with the nearly identical DNA templates with thr attenuator.Results indicate theat in the low concentration of magnesium chloride or high amount of sodium chloride or potassium glutamate,termination by T7,T3,and SP6 RNA polymerases is enhanced.Also, inresponse to high NTP concentration the termination efficiencies of T7 and T3 RNA polymerases are enhanced and that of SP6 RNA polymerase remain constant.