Cunningham P R, Weitzmann C J, Ofengand J
Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110.
Nucleic Acids Res. 1991 Sep 11;19(17):4669-73. doi: 10.1093/nar/19.17.4669.
The 16S ribosomal RNA gene of Escherichia coli was placed under the transcriptional control of consensus and modified T7 promoters and a modified SP6 promoter. Both T7 and SP6 polymerases faithfully transcribed the coding sequence (beginning at the +1 position) of each construct, although SP6 polymerase was five-fold more effective than T7 polymerase in initiating with the AAAUUG... sequence. An appreciable fraction of the SP6 transcript molecules contained additional adenosines in the -1, -2, -3, -4, and -5 positions. The transcripts containing additional residues constituted approximately 40-50% of the total SP6 transcription products. Neither the nature nor extent of the additional residues was affected by replacing the pppA 5'-end by pA. Since the identity of the inserted residues does not correspond to the sequence of the template, these additional nucleosides must result from 'stuttering' of the SP6 enzyme at the -1 to +3 positions during initiation of transcription.
大肠杆菌的16S核糖体RNA基因被置于共有型和修饰型T7启动子以及修饰型SP6启动子的转录控制之下。T7和SP6聚合酶都能忠实地转录每个构建体的编码序列（从+1位置开始），尽管SP6聚合酶以AAAUUG...序列起始时的效率比T7聚合酶高五倍。相当一部分SP6转录本分子在-1、-2、-3、-4和-5位置含有额外的腺苷。含有额外残基的转录本约占SP6转录产物总量的40-50%。用pA取代pppA 5'-末端，既不影响额外残基的性质，也不影响其程度。由于插入残基的身份与模板序列不对应，这些额外的核苷必定是由SP6酶在转录起始时在-1至+3位置的“口吃”导致的。
