Disease relevance of ssrA

• In E. coli, the adaptor SspB tethers ssrA-tagged substrates to the ClpXP protease, causing a modest increase in their rate of degradation [1].
• Using various ssrA alleles, we demonstrate the importance of SsrA charging on the ribosome for controlling Mu prophage repression [2].
• The PAI is 39.5 kb in size, has low %G+C (35%), contains putative integrase and transposase genes, is flanked by att sites, and inserts near a 10Sa RNA gene (ssrA), suggesting it may be of bacteriophage origin [3].
• Both forms of the protein displayed equivalent stability in the slow-growing species Mycobacterium bovis bacille Calmette-Guerin (BCG), suggesting differing recognition of the ssrA-encoded peptides in slow- and fast-growing mycobacteria [4].
• We report that tmRNA is essential in Neisseria gonorrhoeae [5].

High impact information on ssrA

• The tag appears to be added to the carboxyl terminus of the nascent polypeptide chain by cotranslational switching of the ribosome from the damaged messenger RNA to ssrA RNA [6].
• This tripartite structure--an ssrA-tag binding and dimerization domain, a flexible linker, and a short peptide module that docks with ClpX--allows SspB to deliver tagged substrates to ClpXP without interfering with their denaturation or degradation [7].
• ClpXP is a protease involved in DNA damage repair, stationary-phase gene expression, and ssrA-mediated protein quality control [8].
• We report that native Escherichia coli tmRNA interacts specifically with native or synthetic E.coli tRNA alanine (tRNA(Ala)) in vitro, alanine being the first codon of the tmRNA internal open reading frame [9].
• The reading frame of tmRNA is determined differently from all other known reading frames in that the first translated codon is not specified by a particular tRNA anticodon [10].

Chemical compound and disease context of ssrA

• In E. coli tmRNA, the five uridine cleavage sites are located in double-stranded regions [11].
• Amino acid acceptor identity switch of Escherichia coli tmRNA from alanine to histidine in vitro [12].
• To gain more insight about Escherichia coli tmRNA structure, NiCR, a square planar macrocyclic nickel (II) complex, was used to probe guanine N7 exposure [11].

Biological context of ssrA

• Disruption of the gene encoding 10Sa RNA (ssrA) caused a reduction in the rate of cell growth, which was especially apparent at 45 degrees C, and a reduction in motility on semisolid agar [13].
• Analysis of the Escherichia coli Alp phenotype: heat shock induction in ssrA mutants [14].
• We show that sipB391, previously located to the 57-min region of the E. coli chromosome, is a large deletion that extends into the 3' end of ssrA, a gene encoding the small stable 10Sa RNA [15].
• The 10Sa RNA gene (ssrA) has been located between 2,760 and 2,761 kilobases on the E. coli genome [16].
• We find that ssrA mutants alone significantly induce the heat shock response [14].

Anatomical context of ssrA

• These functions are facilitated by transfer-messenger RNA (tmRNA, also called 10Sa RNA or SsrA RNA), a small stable RNA molecule encoded by the SsrA gene found in bacteria, chloroplasts and mitochondria [17].
• The cyanelle of the primitive alga Cyanophora paradoxa is the only photosynthetic organelle where the ribonucleoprotein nature of this enzyme has been functionally proven. tmRNA is another highly structured RNA: it can be aminoacylated with alanine, which is then incorporated into a tag peptide encoded on the same RNA molecule [18].
• tmRNA decreases the bactericidal activity of aminoglycosides and the susceptibility to inhibitors of cell wall synthesis [19].

Associations of ssrA with chemical compounds

• When the G.U pair (G3.U357) in 10Sa RNA, which may be equivalent to the determinant G.U pair of alanine tRNA, was changed to a G.A or G.C pair, the ability to complement the phenotypic mutations of the delta ssrA strain was lost [13].
• We have investigated directionality in the ClpA/ClpP-mediated reaction by using two substrate proteins bearing the COOH-terminal ssrA recognition element, each labeled near the NH(2) or COOH terminus with fluorescent probes [20].
• Although A-site-cleaved mRNAs were not detected, tmRNA-mediated ssrA tagging after SecM glycine 165 was observed [21].
• Inactivation of transfer mRNA (tmRNA) (encoded by ssrA), coupled with a multicopy kanamycin resistance determinant, suppressed both lon phenotypes and restored the rapid degradation of SulA [14].
• The native E.coli tmRNA contains two modified nucleosides, 5-methyluridine and pseudouridine [22].

Physical interactions of ssrA

• Aminoacylated tmRNA from Escherichia coli interacts with prokaryotic elongation factor Tu [23].

Other interactions of ssrA

• Kinetic parameters for tmRNA binding to alanyl-tRNA synthetase and elongation factor Tu from Escherichia coli [24].
• Using RNase H digestion followed by primer extension with reverse transcriptase, two cross-linked sites were identified within the tRNA-like region of tmRNA [25].
• In vitro and in vivo processing of cyanelle tmRNA by RNase P [18].

Analytical, diagnostic and therapeutic context of ssrA

• By PCR analysis and sequencing, it was shown that this integrative element is present in a number of non-O157 STEC serotypes and in non-STEC strains, where it is located at the 3'-end of the chromosomal ssrA gene [26].
• From Escherichia coli cells with a deletion in the ssrA gene that encodes 10Sa RNA after treatment with a mutagen, we isolated two temperature-sensitive mutants, which we designated TS15 and TS101 [27].
• Together with comparative sequence analysis, these findings yielded a three-dimensional model of the tRNA-like domain of E. coli tmRNA [25].
• Covariations, identified by sequence alignment with nine other tmRNA sequences, suggest the presence of several tertiary interactions, including pseudoknots [28].
• Gel mobility shift assays demonstrated that tmRNA(Delta90-299), a truncated tmRNA derivative lacking pseudoknots 2-4, has the same affinity for the Escherichia coli and Aquifex aeolicus SmpB proteins as the intact E. coli tmRNA [29].

References