Expression Archaebacteria

This rule-based system allows expressing the membership criteria for each protein family in a formal language. Furthermore, subfamilies have been introduced to meet the SWISS-PROT standard more closely. For example, the ribosomal protein LI family contains eukaryotes as well as prokaryotes. But the annotation added to TrEMBL entries of this family obviously depends on the taxonomic kingdom. The description reads "50S RIBOSOMAL PROTEIN Ll" for prokaryotes, archaebacteria, chloroplasts, and cyanelles, and "60S ribosomal protein lioa" for nuclear encoded proteins of eukaryotes. 

The 1980 view assumed that the prokaryote-to-eukaryote transition occurred via gradualist mechanisms such as point mutation and hence did not involve symbiosis at all (van Valen and Maiorana 1980 Doolittle 1980) and culminated with a cell that possessed a nucleus, but lacked mitochondria. This is what Doolittle (1998) has called the standard model . In this view, mitochondria are interpreted as a small tack-on to, and mechanistically unrelated to, the process that made eukaryotic cells nucleated and complex (Cavalier-Smith 2002). In the standard model, mitochondria (and chloro-plasts) are descended from endosymbionts, but the nuts-and-bolts of the prokaryote-to-eukaryote transition (the origin of eukaryote-specific traits) was seen as having occurred independently from, and prior to, the origin of mitochondria. The paper by van Valen and Maiorana (1980) expresses this view in clear physiological terms the host was assumed to be an amoeboid, anaerobic, fermenting cell related to archaebacteria, the advantage of the mitochondrial endosymbiont was to supply ATP. 

For many of the extreme thermophiles defined media are not yet available, enzyme yields are low and some of the archaebacteria are very fastidious with low cell yields being obtained. Cloning and expression of the enzymes in E. coli (for instance) can obviate these problems and notable advances in this area have occurred very recently (see Sect, 6). 

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