Bacterial Argonaute Proteins Aid Cell Division in the Presence of Topoisomerase Inhibitors in Escherichia coli.

Prokaryotic Argonaute (pAgo) proteins are guide-dependent nucleases that function in host defense against invaders. Recently, it was shown that TtAgo from Thermus thermophilus also participates in the completion of DNA replication by decatenating chromosomal DNA. Here, we show that two pAgos from cyanobacteria Synechococcus elongatus (SeAgo) and Limnothrix rosea (LrAgo) are active in heterologous Escherichia coli and aid cell division in the presence of the gyrase inhibitor ciprofloxacin, depending on the host double-strand break repair machinery.

Bacterial Argonaute nucleases reveal different modes of DNA targeting in vitro and in vivo.

Prokaryotic Argonaute proteins (pAgos) are homologs of eukaryotic Argonautes (eAgos) and are also thought to play a role in cell defense against invaders. However, pAgos are much more diverse than eAgos and little is known about their functional activities and target specificities in vivo. Here, we describe five pAgos from mesophilic bacteria that act as programmable DNA endonucleases and analyze their ability to target chromosomal and invader DNA.

DNA targeting and interference by a bacterial Argonaute nuclease.

Members of the conserved Argonaute protein family use small RNA guides to locate their mRNA targets and regulate gene expression and suppress mobile genetic elements in eukaryotes. Argonautes are also present in many bacterial and archaeal species. Unlike eukaryotic proteins, several prokaryotic Argonaute proteins use small DNA guides to cleave DNA, a process known as DNA interference.

Genome-wide DNA sampling by Ago nuclease from the cyanobacterium .

Members of the conserved Argonaute (Ago) protein family provide defence against invading nucleic acids in eukaryotes in the process of RNA interference. Many prokaryotes also contain Ago proteins that are predicted to be active nucleases; however, their functional activities in host cells remain poorly understood. Here, we characterize the and properties of the SeAgo protein from the mesophilic cyanobacterium .

Programmable DNA cleavage by Ago nucleases from mesophilic bacteria Clostridium butyricum and Limnothrix rosea.

Argonaute (Ago) proteins are key players in RNA interference in eukaryotes, where they function as RNA-guided RNA endonucleases. Prokaryotic Argonautes (pAgos) are much more diverse than their eukaryotic counterparts but their cellular functions and mechanisms of action remain largely unknown. Some pAgos were shown to use small DNA guides for endonucleolytic cleavage of complementary DNA in vitro.

Biological and Evolutionary Significance of Terminal Extensions of Mitochondrial Translation Initiation Factor 3.

Protein biosynthesis in mitochondria is organized in a bacterial manner. However, during evolution, mitochondrial translation mechanisms underwent many organelle-specific changes. In particular, almost all mitochondrial translation factors, being orthologous to bacterial proteins, are characterized by some unique elements of primary or secondary structure.

60S dynamic state of bacterial ribosome is fixed by yeast mitochondrial initiation factor 3.

The processes of association and dissociation of ribosomal subunits are of great importance for the protein biosynthesis. The mechanistic details of these processes, however, are not well known. In bacteria, upon translation termination, the ribosome dissociates into subunits which is necessary for its further involvement into new initiation step.

Aim-less translation: loss of Saccharomyces cerevisiae mitochondrial translation initiation factor mIF3/Aim23 leads to unbalanced protein synthesis.

The mitochondrial genome almost exclusively encodes a handful of transmembrane constituents of the oxidative phosphorylation (OXPHOS) system. Coordinated expression of these genes ensures the correct stoichiometry of the system's components. Translation initiation in mitochondria is assisted by two general initiation factors mIF2 and mIF3, orthologues of which in bacteria are indispensible for protein synthesis and viability.

An evolutionary ratchet leading to loss of elongation factors in eukaryotes.

Background: The GTPase eEF1A is the eukaryotic factor responsible for the essential, universal function of aminoacyl-tRNA delivery to the ribosome. Surprisingly, eEF1A is not universally present in eukaryotes, being replaced by the paralog EFL independently in multiple lineages. The driving force behind this unusually frequent replacement is poorly understood.

Mitochondrial translation initiation machinery: conservation and diversification.

The highly streamlined mitochondrial genome encodes almost exclusively a handful of transmembrane components of the respiratory chain complex. In order to ensure the correct assembly of the respiratory chain, the products of these genes must be produced in the correct stoichiometry and inserted into the membrane, posing a unique challenge to the mitochondrial translational system. In this review we describe the proteins orchestrating mitochondrial translation initiation: bacterial-like general initiation factors mIF2 and mIF3, as well as mitochondria-specific components - mRNA-specific translational activators and mRNA-nonspecific accessory initiation factors.

Evolutionary and genetic analyses of mitochondrial translation initiation factors identify the missing mitochondrial IF3 in S. cerevisiae.

Mitochondrial translation is essentially bacteria-like, reflecting the bacterial endosymbiotic ancestry of the eukaryotic organelle. However, unlike the translation system of its bacterial ancestors, mitochondrial translation is limited to just a few mRNAs, mainly coding for components of the respiratory complex. The classical bacterial initiation factors (IFs) IF1, IF2 and IF3 are universal in bacteria, but only IF2 is universal in mitochondria (mIF2).

Single molecule tracking fluorescence microscopy in mitochondria reveals highly dynamic but confined movement of Tom40.

Tom40 is an integral protein of the mitochondrial outer membrane, which as the central component of the Translocase of the Outer Membrane (TOM) complex forms a channel for protein import. We characterize the diffusion properties of individual Tom40 molecules fused to the photoconvertable fluorescent protein Dendra2 with millisecond temporal resolution. By imaging individual Tom40 molecules in intact isolated yeast mitochondria using photoactivated localization microscopy with sub-diffraction limited spatial precision, we demonstrate that Tom40 movement in the outer mitochondrial membrane is highly dynamic but confined in nature, suggesting anchoring of the TOM complex as a whole.