| Summary: | 碩士 === 國立陽明大學 === 生命科學暨基因體科學研究所 === 99 === Several small non-coding RNAs (sRNAs) have been identified in E. coli that act by various mechanisms and are involved in a wide range of physiological responses. The majority of sRNAs characterized to date interact with mRNA targets by base pairing, having either extensive (cis-encoded) or limited (trans-encoded) complementarities with their targets. Although sRNAs are involved in transcriptional regulation, they primarily act on their targets at the post-transcriptional level, which may result in destabilization or stabilization of mRNAs. Here we discovered that the sRNA DsrA may play a role in response to incoming plasmid and inhibit DNA plasmid replication in bacteria. It is known that two different regions in the DsrA sequence ranging from 15 to 20 nucleotides can target multiple transcripts with different modes of regulations. Searching for sequence complementarities of these two DsrA regions with known sRNAs in E. coli, we found that the antisense RNA RNAI of ColE1-type plasmids has a putative binding site for DsrA. By introducing a non-ColE1 type plasmid expressing RNAI named pCML108 into E. coli MG1655 wild-type and 岛dsrA strains, we found a decrease in RNAI expression as well as in RNAI stability in the 岛dsrA strain. Overexpression of DsrA also decreases the ColE1 plasmid copy number. We also found that introducing pCM128 plasmid (without RNAI expression) into E.coli can prolong the stability of DsrA, and introducing pCML108 (with RNAI expression) prolongs DsrA stability even more. Whether the RNA chaperone Hfq plays a role in this DsrA-RNAI regulation will be further addressed. The regulatory mechanism between these two sRNAs will be further examined by mutating the putative binding sites. In summary, this finding reveals a novel sRNA regulatory role.
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