Botany Department, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
J Biol Chem. 2010 Feb 19;285(8):5196-203. doi: 10.1074/jbc.M109.058545. Epub 2009 Nov 30.
The chloroplast genome of a dinoflagellate consists of a group of small circular DNA molecules (minicircles), most of which carry a single gene. With RT-PCR, primer extension, and Northern analyses, we show that the entire minicircle is transcribed and that some minicircles can produce RNAs larger than themselves. Using an RNA ligase-mediated rapid amplification of cDNA ends method, we were able to detect large processed precursors that are generated by endonucleolytic cleavage of an even longer molecule. This cleavage produces the mature mRNA 3'-end and at the same time the 5'-end of the precursor. The tRNAs encoded by the petD and psbE minicircles appear to be processed in the same way. We propose a "rolling circle" model for chloroplast transcription in which transcription would proceed continuously around the minicircular DNA to produce transcripts larger than the minicircle itself. These transcripts would be further processed into discrete mature mRNAs and tRNAs.
甲藻的叶绿体基因组由一组小型环状 DNA 分子（迷你环）组成，其中大多数携带单个基因。通过 RT-PCR、引物延伸和 Northern 分析，我们表明整个迷你环都被转录，并且一些迷你环可以产生大于自身的 RNA。使用 RNA 连接酶介导的 cDNA 末端快速扩增方法，我们能够检测到由更长的分子内切切割产生的大加工前体。这种切割产生成熟 mRNA 的 3' 端，同时也是前体的 5' 端。由 petD 和 psbE 迷你环编码的 tRNA 似乎以相同的方式进行加工。我们提出了叶绿体转录的“滚环”模型，其中转录将在迷你环 DNA 周围连续进行，以产生大于迷你环本身的转录本。这些转录本将进一步加工成离散的成熟 mRNA 和 tRNA。
