Transferring Eukaryotic Genes

Fig. 10.11 The modified tree of life still has the usual tree-like structure and also confirms that the eukaryotes originally took over mitochondria and chloroplasts from bacteria. It does, however, also show a network of links between the branches. The many interconnections indicate a frequent transfer of genes between unicellular organisms. The modified tree of life is not derived, as had previously been assumed, from a single cell (the hypothetical primeval cell ). Instead, the three main kingdoms are more likely to have developed from a community of primitive cells with different genomes (Doolittle, 2000)...

The outcome of, or perhaps the support for, the endosymbiont transferring its genes to the nucleus was the evolution of new machinery in the eukaryotic cell to send the nuclear-encoded proteins back to the degenerate endosymbiont to allow the latter to function. Moreover, it is of note that the large majority of extant mitochondrial proteins are not of endosymbiotic or a-proteobacterial origin. These proteins have either been recruited... 

Nixon JE et al. (2002a) Evidence for lateral transfer of genes encoding ferredoxins, nitroreductases, NADH oxidase, and alcohol dehydrogenase 3 from anaerobic prokaryotes to Giardia lamblia and Entamoeba histolytica. Eukaryot Cell 1 181-190 Nixon JE et al. (2002b) A spliceosomal intron in Giardia lamblia. Proc Natl Acad Sci USA 99 3701-3705... 

A number of different viruses have been used to transfer foreign genes into eukaryotic cells and also to create stable plasmids for cloning. One of the first was the 5380 bp SV40. The relatively small size of SV40... 

Katsel, P.L. and Greenstein, R.J. (2000) Eukaryotic gene transfer with liposomes effect of differences in lipid structure. Biotechnol. Ann. Rev., 5, 197-220. 

All classes of RNA transcripts must be processed into mature species. The reactions include several types Nucleolytic cleavage, as in the separation of the mature rRNA species from the primary transcript of RNA polymerase I action Chain extension (non-template-directed), as in the synthesis or regeneration of the common CCA sequence at the 3 end of transfer RNAs or of PolyA at the 3 end of mRNAs and Nucleotide modification, for example, the synthesis of methylated nucleotides in tRNA or rRNA. These reactions are a feature of both prokaryotic and eukaryotic gene expression, and the biological consequences are diverse. For example, modified nucleotides can affect the way in which a tRNA recognizes different codons. 

Methylation underlies several important biological processes, including restriction and modification, mismatch error correction (a DNA repair process), and the control of eukaryotic gene expression. S-Adenosylmethionine (AdoMet) is the substrate for methylation of both RNA and DNA. Methylation occurs at the polynucleotide level, with transfer of a methyl group from AdoMet to a nucleotide residue. 

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