By S1 nuclease protection experiments and primer extension analysis, we determined precisely the cap and polyadenylation sites of transcripts from the four genes of the yeast 2 micron circle plasmid, as well as those of other plasmid transcripts of unknown function. In addition, we used deletion analysis to identify sequences necessary for polyadenylation in plasmid transcripts. Our results indicate that plasmid genes constitute independent transcription units and that plasmid mRNAs are not derived by extensive processing of precursor transcripts. In addition, we found that the D coding region of 2 micron circle is precisely encompassed by a polyadenylated transcript, suggesting that this coding region constitutes a functional plasmid gene. Our identification of the position of plasmid polyadenylation sites and of sequences necessary for polyadenylation provides support for a tripartite signal for polyadenylation as proposed by Zaret and Sherman (K.S. Zaret and F. Sherman, Cell 28:563-573, 1982). Finally, these data highlight salient features of the transcriptional regulatory circuitry that underlies the control of plasmid maintenance in the cell.
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机译：通过S1核酸酶保护实验和引物延伸分析，我们从酵母2微米圆质粒的四个基因以及功能未知的其他质粒转录本中准确确定了转录本的帽盖和聚腺苷酸化位点。另外，我们使用缺失分析来鉴定质粒转录物中聚腺苷酸化所必需的序列。我们的结果表明，质粒基因构成独立的转录单位，而质粒mRNA并非通过大量加工前体转录物而获得。此外，我们发现2微米圈的D编码区正好被聚腺苷酸化的转录物所包围，表明该编码区构成了功能质粒基因。如Zaret和Sherman（K.S. Zaret and F.Sherman，Cell 28：563-573，1982）所提出的，我们对质粒聚腺苷酸化位点位置和聚腺苷酸化必需序列的鉴定为聚腺苷酸化的三重信号提供了支持。最后，这些数据突出了转录调节电路的显着特征，这些特征是控制细胞中质粒维持的基础。
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