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 Such genes seem to have been replaced by homologues in the nuclear (host) genome.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...

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Not I linking clones contain sequences flanking Not I recognition sites and were previously shown to be tightly associated with CpG islands and genes. To directly assess the value of Not I clones in genome research, high density grids with 50 000 Not I linking clones originating from six representative Not I linking libraries were constructed. Altogether, these libraries contained nearly 100 times the total number of Not I sites in the human genome. A total of 3437 sequences flanking Not I sites were generated. Analysis of 3265 unique sequences demonstrated that 51% of the clones displayed significant protein similarity to SWISSPROT and TREMBL database proteins based on MSPcrunch filtering with stringent parameters. Of the 3265 sequences, 1868 (57.2%) were new sequences, not present in the EMBL and EST databases (similarity < or =90%). Among these new sequences, 795 (24.3%) showed similarity to known proteins and 712 (21.8%) displayed an identity of >75% at the nucleotide level to sequences from EMBL or EST databases. The remaining 361 (11.1%) sequences were completely new, i.e. <75% identical. The work also showed tight, specific association of Not I sites with the first exon and suggest that the so-called 3' ESTs can actually be generated from 5'-ends of genes that contain Not I sites in their first exon.

Due to the importance of boiling heat transfer in general, and boiling crisis in particular, for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems, extensive efforts have been made in the past to develop a variety of methods and tools to evaluate the boiling heat transfer coefficient and to assess the onset of temperature excursion and critical heat flux (CHF) at various operating conditions of boiling channels. The objective of this paper is to present mathematical modeling concepts behind the development of mechanistic multidimensional models of low-quality forced convection boiling, including the mechanisms leading to temperature excursion and the onset of CHF.