Polyadenylation contributes to the destabilization of bacterial mRNA. We have investigated the role of polyadenylation in the degradation of RNA by the purified Escherichia coli degradosome in vitro. RNA molecules with 3'-ends incorporated into a stable stem-loop structure could not readily be degraded by purified polynucleotide phosphorylase or by the degradosome, even though the degradosome contains active RhlB helicase which normally facilitates degradation of structured RNA. The exoribonucleolytic activity of the degradosome was due to polynucleotide phosphorylase, rather than the recently reported exonucleolytic activity exhibited by a purified fragment of RNase E (Huang, H., Liao, J., and Cohen, S. N. (1998) Nature 391, 99-102). Addition of a 3'-poly(A) tail stimulated degradation by the degradosome. As few as 5 adenosine residues were sufficient to achieve this stimulation, and generic sequences were equally effective. The data show that the degradosome requires a single-stranded "toehold" 3' to a secondary structure to recognize and degrade the RNA molecule efficiently; polyadenylation can provide this single-stranded 3'-end. Significantly, oligo(G) and oligo(U) tails were unable to stimulate degradation; for oligo(G), at least, this is probably due to the formation of a G quartet structure which makes the 3'-end inaccessible. The inaccessibility of 3'-oligo(U) sequences is likely to have a role in stabilization of RNA molecules generated by Rho-independent terminators.
"The 5 0 region of AsxR is complementary to the single-stranded loop of the FnrS Rho-independent terminator. FnrS was destabilized by AsxR, consistent with AsxR hybridization unfolding the terminator stem that protects the 3 0 end from exonucleolytic attack (Blum et al., 1999; Cisneros et al., 1996; Figueroa-Bossi et al., 2009). A similar mechanism of sRNA destabilization has been proposed for ChiX (MicM), an sRNA that is destabilized by an intercistronic region of the chbBC transcript with complementarity to the terminator stem of ChiX (Figueroa-Bossi et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: In bacteria, Hfq is a core RNA chaperone that catalyzes the interaction of mRNAs with regulatory small RNAs (sRNAs). To determine in vivo RNA sequence requirements for Hfq interactions, and to study riboregulation in a bacterial pathogen, Hfq was UV crosslinked to RNAs in enterohemorrhagic Escherichia coli (EHEC). Hfq bound repeated trinucleotide motifs of A-R-N (A-A/G-any nucleotide) often associated with the Shine-Dalgarno translation initiation sequence in mRNAs. These motifs overlapped or were adjacent to the mRNA sequences bound by sRNAs. In consequence, sRNA-mRNA duplex formation will displace Hfq, promoting recycling. Fifty-five sRNAs were identified within bacteriophage-derived regions of the EHEC genome, including some of the most abundant Hfq-interacting sRNAs. One of these (AgvB) antagonized the function of the core genome regulatory sRNA, GcvB, by mimicking its mRNA substrate sequence. This bacteriophage-encoded "anti-sRNA" provided EHEC with a growth advantage specifically in bovine rectal mucus recovered from its primary colonization site in cattle.
"). RssB 과발현에 의한 세균 성장 저하 현 상은 RNA 대사에 핵심적인 기능을 하는 poly(A) polymerase I (PAP I) 활성과 관련이 있다(Carabetta et al., 2009, 2010). PAP I 은 RNA의 3ʹ 말단에 poly(A)를 형성하는 효소로서 궁극적으 로 mRNA의 파괴를 촉진시키며 polyadenylation 역시 mRNA 의 분해를 촉진시킨다(Blum et al., 1999; Mohanty and Kushner, 1999). RssB는 PAP I의 세포 내 위치변화(세포막과 세포질)와 PAP-I degradosome 유지에 핵심적인 역할을 한다(Carabetta et al., 2009, 2010 "
[Show abstract][Hide abstract] ABSTRACT: Against environmental stresses, many bacteria utilize the alternate sigma factor RpoS that induces transcription of the specific set of genes helpful in promoting bacterial survival. Intracellular levels of RpoS are determined mainly by its turnover through proteolysis of ClpXP protease. Delivery of RpoS to ClpXP strictly requires the adaptor protein RssB. The two-component-type response regulator RssB constantly interacts with RpoS, but diverse environmental changes inhibit this interaction through modification of RssB activity, which increases RpoS levels in bacteria. This review discusses and summarizes recent findings on regulatory factors in RssB-RpoS interactions, including IraD, IraM, IraP anti-adaptor proteins of RssB and phosphorylation of N-terminal receiver domain of RssB. New information shows that the coordinated regulation of RssB activity in controlling RpoS turnover confers efficient bacterial defense against stresses.
Korean Journal of Microbiology 09/2013; 49(3). DOI:10.7845/kjm.2013.3057
"Its activity is inhibited by the formation of stable stem-loops. Polyadenylation of the RNases in chloroplasts | 1667 transcript 3# end can help overcome this problem, thus speeding up RNA degradation (Blum et al., 1999). Chloroplast PNPase (At3g03710) is composed of two exoribonucleolytic RNase PH core domains, which are involved in RNA degradation and polymerization, together with an RNA-binding S1 domain that has a high affinity for poly(A) tails (Yehudai-Resheff et al., 2003). "
[Show abstract][Hide abstract] ABSTRACT: Chloroplast biogenesis requires constant adjustment of RNA homeostasis under conditions of on-going developmental and environmental change and its regulation is achieved mainly by post-transcriptional control mechanisms mediated by various nucleus-encoded ribonucleases. More than 180 ribonucleases are annotated in Arabidopsis, but only 17 are predicted to localize to the chloroplast. Although different ribonucleases act at different RNA target sites in vivo, most nucleases that attack RNA are thought to lack intrinsic cleavage specificity and show non-specific activity in vitro. In vivo, specificity is thought to be imposed by auxiliary RNA-binding proteins, including members of the huge pentatricopeptide repeat family, which protect RNAs from non-specific nucleolytic attack by masking otherwise vulnerable sites. RNA stability is also influenced by secondary structure, polyadenylation, and ribosome binding. Ribonucleases may cleave at internal sites (endonucleases) or digest successively from the 5' or 3' end of the polynucleotide chain (exonucleases). In bacteria, RNases act in the maturation of rRNA and tRNA precursors, as well as in initiating the degradation of mRNAs and small non-coding RNAs. Many ribonucleases in the chloroplasts of higher plants possess homologies to their bacterial counterparts, but their precise functions have rarely been described. However, many ribonucleases present in the chloroplast process polycistronic rRNAs, tRNAs, and mRNAs. The resulting production of monocistronic, translationally competent mRNAs may represent an adaptation to the eukaryotic cellular environment. This review provides a basic overview of the current knowledge of RNases in plastids and highlights gaps to stimulate future studies.
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