Discovery of a rhizobial RNA that is essential for symbiotic root nodule development

Zomorodipour

et al. 1998

Nature

1,527

1,093

We describe here the complete genome sequence (1,111,523 base pairs) of the obligate intracellular parasite Rickettsia prowazekii, the causative agent of epidemic typhus. This genome contains 834 protein-coding genes. The functional pro®les of these genes show similarities to those of mitochondrial genes: no genes required for anaerobic glycolysis are found in either R. prowazekii or mitochondrial genomes, but a complete set of genes encoding components of the tricarboxylic acid cycle and the respiratory-chain complex is found in R. prowazekii. In effect, ATP production in Rickettsia is the same as that in mitochondria. Many genes involved in the biosynthesis and regulation of biosynthesis of amino acids and nucleosides in free-living bacteria are absent from R. prowazekii and mitochondria. Such genes seem to have been replaced by homologues in the nuclear (host) genome. The R. prowazekii genome contains the highest proportion of non-coding DNA (24%) detected so far in a microbial genome. Such non-coding sequences may be degraded remnants of`neutralized' genes that await elimination from the genome. Phylogenetic analyses indicate that R. prowazekii is more closely related to mitochondria than is any other microbe studied so far.The Rickettsia are a-proteobacteria that multiply in eukaryotic cells only. R. prowazekii is the agent of epidemic, louse-borne typhus in humans. Three features of this endocellular parasite deserve our attention. First, R. prowazekii is estimated to have infected 20±30 million humans in the wake of the First World War and killed another few million following the Second World War (ref. 1). Because it is the descendent of free-living organisms 2±4 , its genome provides insight into adaptations to the obligate intracellular lifestyle, with probable practical value. Second, phylogenetic analyses based on sequences of ribosomal RNA and heat-shock proteins indicate that mitochondria may be derived from the aproteobacteria 5,6 . Indeed, the closest extant relatives of the ancestor to mitochondria seem to be the Rickettsia 7±10 . That modern Rickettsia favour an intracellular lifestyle identi®es these bacteria as the sort of organism that might have initiated the endosymbiotic scenario leading to modern mitochondria 11 . Finally, the genome of R. prowazekii is a small one, containing only 1,111,523 base pairs (bp). Its phylogenetic placement and many other characteristics identify it as a descendant of bacteria with substantially larger genomes 2±4 . Thus Rickettsia, like mitochondria, are good examples of highly derived genomes, the products of several types of reductive evolution.The genome sequence of R. prowazekii indicates that these three features may be related. For example, prokaryotic genomes evolving within a cell dominated by a much larger, eukaryote genome and constrained by bottle-necked population dynamics will tend to lose genetic information 12,13 . Predictable sets of expendable genes will tend to disappear from the prokaryotic genome when they are made redundant by the activit...

Section: General Features Of the Genomementioning

confidence: 99%

Section: Transcription and Translationmentioning

confidence: 99%

See 1 more Smart Citation

The genome sequence of Rickettsia prowazekii and the origin of mitochondria

Zomorodipour

et al. 1998

Nature

1,527

1,093

“…With quantitative kinetic experiments we determined that after a shift from 28 to 43ЊC the amount of rpoH 2 mRNA originating from P 1 rapidly decreased, reaching 60% of the original level at 15 min and less than 40% at 2 h after the temperature upshift (data not shown). The amount of sra RNA, which does not respond to heat treatment, served as an internal control and allowed the relative quantification of the rpoH 2 mRNA (Ebeling et al, 1991;Babst et al, 1996). The additional bands just below the T 1 product ( Fig.…”

Section: Transcriptional Mapping Of the Rpoh 2 Gene Regionmentioning

confidence: 99%

Three disparately regulated genes for σ³²‐like transcription factors in Bradyrhizobium japonicum

Narberhaus

Krummenacher

Fischer

et al. 1997

Molecular Microbiology

119

Proc. Natl. Acad. Sci. U.S.A.

“…tmRNA activity is essential for growth of Neisseria gonorrhoeae (10), Haemophilus influenzae (11), and species of Mycoplasma (12). tmRNA mutants in Salmonella enterica (13,14) and Yersinia pseudotuberculosis (15) have decreased virulence, and mutants of Caulobacter crescentus (16) and Bradyrhizobium japonicum (17) lacking tmRNA activity have developmental defects. In Escherichia coli (18)(19)(20) and Bacillus subtilis (21,22), tmRNA is required for optimal growth under a variety of stress conditions.…”

mentioning

confidence: 99%

Proteomic identification of tmRNA substrates

Hong

Lessner

Mahen

et al. 2007

The tmRNA-SmpB system releases ribosomes stalled on truncated mRNAs and tags the nascent polypeptides to target them for proteolysis. In many species, mutations that disrupt tmRNA activity cause defects in growth or development. In Caulobacter crescentus cells lacking tmRNA activity there is a delay in the initiation of DNA replication, which disrupts the cell cycle. To understand the molecular basis for this phenotype, 73 C. crescentus proteins were identified that are tagged by tmRNA under normal growth conditions. Among these substrates, proteins involved in DNA replication, recombination, and repair were overrepresented, suggesting that misregulation of these factors in the absence of tmRNA activity might be responsible for the delay in initiation of DNA replication. Analysis of the tagging sites within these substrates revealed a conserved nucleotide motif 5 of the tagging site, which is required for wild-type tmRNA tagging.bacterial cell cycle ͉ proteolysis ͉ trans-translation