Stalled bacterial ribosomes are freed when they switch to the translation of transfer-messenger RNA (tmRNA). This process requires the tmRNA-binding and ribosome-binding cofactor SmpB, a ␤-barrel protein with a protruding C-terminal tail of unresolved structure. Some plastid genomes encode tmRNA, but smpB genes have only been reported from bacteria. Here we identify smpB in the nuclear genomes of both a diatom and a red alga encoding a signal for import into the plastid, where mature SmpB could activate tmRNA. Diatom SmpB was active for tmRNA translation with bacterial components in vivo and in vitro, although less so than Escherichia coli SmpB. The tail-truncated diatom SmpB, the hypothetical product of a misspliced mRNA, was inactive in vivo. Tail-truncated E. coli SmpB was likewise inactive for tmRNA translation but was still able to bind ribosomes, and its affinity for tmRNA was only slightly diminished. This work suggests that SmpB is a universal cofactor of tmRNA. It also reveals a tail-dependent role for SmpB in tmRNA translation that supersedes a simple role of linking tmRNA to the ribosome, which the SmpB body alone could provide.

P311 is an 8-kDa intracellular protein that is highly conserved across species and is expressed in the nervous system as well as in vascular and visceral smooth muscle cells. P311-null (P311 -/-) mice display learning and memory defects, but alterations in their vasculature have not been previously described. Here we report that P311 -/-mice are markedly hypotensive with accompanying defects in vascular tone and VSMC contractility. Functional abnormalities in P311 -/-mice resulted from decreased total and active levels of TGF-β1, TGF-β2, and TGF-β3 that arise as a specific consequence of decreased translation. Vascular hypofunctionality was fully rescued in vitro and in vivo by exogenous TGF-β1-TGF-β3. Conversely, P311-transgenic (P311 TG ) mice had elevated levels of TGF-β1-TGF-β3 and subsequent hypertension. Consistent with findings attained in mouse models, arteries recovered from hypertensive human patients displayed increased P311 expression. Thus, we identified P311 as the first protein known to modulate TGF-β translation and the first pan-regulator of TGF-β expression under steady-state conditions. Together, our findings point to P311 as a critical blood pressure regulator and establish a potential link between P311 expression and the development of hypertensive disease.

tmRNA combines tRNA and mRNA properties and helps bacteria to cope with stalled ribosomes. Its termini normally pair in the tRNA domain, closing the mRNA portion into a looping domain. A striking variation is a two-piece form that effectively breaks open the mRNA domain loop, resulting from independent gene permutation events in alphaproteobacteria and cyanobacteria. Convergent evolution to a similar form in separate bacterial lineages suggests that loop-opening benefits tmRNA function. This argument is strengthened by the discovery of a third bacterial lineage with a loop-opened two-piece tmRNA. Whereas most betaproteobacteria have one-piece tmRNA, a permuted tmRNA gene was found for Dechloromonas aromatica and close relatives. Correspondingly, two tmRNA pieces were identified, at approximately equal abundance and at a level one-fifteenth that of ribosomes, a 189 nt mRNA piece and a 65 nt aminoacylatable piece. Together these pieces were active with purified Escherichia coli translational components, but not alone. The proposed secondary structure combines common tmRNA features differently from the structures of other two-piece forms. The origin of the gene is unclear; horizontal transfer may be indicated by the similarity of the tRNA domain to that from a cyanobacterial two-piece tmRNA, but such transfer would not appear simple since the mRNA domain is most similar to that of other betaproteobacteria.

tmRNA employs both tRNA-like and mRNA-like properties as it rescues stalled bacterial ribosomes, while targeting the defective mRNA and incomplete nascent protein for degradation. We describe variation of the tmRNA gene (ssrA) and how it informs tmRNA structure and function. Endosymbiont tmRNAs tend to lose secondary structure and length in the mRNA-like region as nucleotide composition drifts with that of the whole genome. A dramatic gene structure variation is circular permutation, which produces two-piece tmRNAs in three bacterial lineages; new sequences blur these lineages. We present evidence that Sinorhizobium two-piece tmRNA retains the 5'-triphosphate of transcriptional initiation and predict a new structure at the 5' end of cyanobacterial two-piece tmRNA precursor. ssrA is a target for some mobile DNAs and a passenger on others. It has been found interrupted (but not functionally disrupted) by mobile elements such as group I introns, genomic islands and palindromic elements. The alphaproteobacterial permuted genes are significantly less frequently interrupted by genomic islands than are their standard counterparts, yet are a hotspot for insertion or swapping of rickettsial palindromic elements, in contrast to other rickettsial loci that show steady decay of a single ancestral element. Bacteriophages, plasmids and genomic islands can carry tmRNA genes; we describe a native bacterial ssrA disrupted by insertion of a genomic island that carries its own ssrA, a genome encoding both one-and two-piece tmRNA, and a phage encoding a tmRNA variant lacking the mRNA-like function, which may counteract host tmRNA during infection.

Cedecea neteri, a member of the Enterobacteriaceae family, has only been identified as a human pathogen in a few previous clinical cases, thus complicating assessment of this organism's pathogenicity and medical relevance. Documented infections attributed to C. neteri primarily involved bacteremia in severely immunocompromised patients. We report a rare case of urinary catheter colonization by a multidrug-resistant C. neteri strain in a patient of advanced age with benign prostatic hyperplasia and other chronic comorbidities. This C. neteri isolate was resistant or intermediate to second-generation cephalosporins, penicillins, and certain β-lactamase inhibitor/β-lactam combinations. Analysis of whole genome sequence information for a representative C. neteri strain indicated the presence of multiple open reading frames with sequence similarity to β-lactamases, including a chromosome-encoded AmpC β-lactamase and metallo-β-lactamases, consistent with the resistance phenotype of this bacterium. The presence of an AmpR homolog suggests that the C. neteriampC may be inducible in response to β-lactam exposure. Molecular insights into antibiotic resistance traits of this emerging opportunistic pathogen will be important for administering adequate antibiotic treatment to ensure favorable patient outcomes.