Squires C, Krainer A, Barry G, Shen W F, Squires C L
Nucleic Acids Res. 1981 Dec 21;9(24):6827-40. doi: 10.1093/nar/9.24.6827.
We have determined the DNA sequence surrounding the transcription terminator following rpoC, the gene that codes for the beta' subunit of RNA polymerase in E. coli K12. The 2044 bp sequence obtained contains the distal 335 codons of rpoC followed by a 212 bp non-coding region and a second open reading frame (ORFa) of 179 codons. The final 181 nucleotides of the sequence form the 5' end of a third open reading frame (ORFb). The in vivo 3' end of the rpoC mRNA was located by analysis of RNA/DNA hybrids cleaved with nuclease S1 (S1 mapping). These results indicated that the major transcription termination of the rplJL-rpoBC transcription unit occurs a short distance past the translation stop codon for rpoC. Four regions of symmetry, suggesting secondary structure in the mRNA, were found in the DNA sequence near the rpoC translation termination codon. The last of these hairpin structures is similar to other rho-independent transcription terminators and its 3' end coincides with the end of the rpoC mRNA as predicted by S1-mapping. Inspection of the open reading frames indicates that rpoC uses a high percentage of codons that are recognized by the major tRNA species of E. coli while ORFa and ORFb contain many codons recognized by minor tRNA species. ORFa specifies a very basic peptide.
我们已经确定了大肠杆菌K12中RNA聚合酶β'亚基编码基因rpoC下游转录终止子周围的DNA序列。获得的2044 bp序列包含rpoC的335个远端密码子，随后是一个212 bp的非编码区和一个179个密码子的第二个开放阅读框（ORFa）。该序列的最后181个核苷酸构成第三个开放阅读框（ORFb）的5'端。通过对用核酸酶S1切割的RNA/DNA杂交体进行分析（S1图谱分析），确定了rpoC mRNA在体内的3'端。这些结果表明，rplJL - rpoBC转录单元的主要转录终止发生在rpoC翻译终止密码子之后的短距离处。在rpoC翻译终止密码子附近的DNA序列中发现了四个对称区域，提示mRNA中存在二级结构。这些发夹结构中的最后一个与其他不依赖ρ因子的转录终止子相似，其3'端与S1图谱预测的rpoC mRNA的末端一致。对开放阅读框的检查表明，rpoC使用了高比例的由大肠杆菌主要tRNA种类识别的密码子，而ORFa和ORFb包含许多由次要tRNA种类识别的密码子。ORFa指定了一种非常碱性的肽。
