Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 42

Prokaryotic organisms of the distant past are perhaps the ancestors of almost all membrane-bound organelles that are found today inside the eukaryotic cells. Among the membrane-bound organelles, some contain their own genome and others lost their genome throughout evolution [103]. The adaptation to the intracellular environment led to the loss of many of the original genes accumulated for environmental survival. Other important genes from the organelles have been transferred to the nucleus over the evolutionary timeline. Organellar DNA transfer to the nucleus is a known process by which, during evolution, some critical genes of the organelles are moved for preservation and synchronization of cell division [104, 105]. But why preservation ? The DNA mutation rate is lower in the nucleus. In some important organelles, high concentrations of reactive oxygen species (ROS) can lead to oxidative stress and DNA damage [106, 107]. Thus, the relocation of a gene from the organelle to the nucleus enables a more secure conservation over time. Moreover, the transfer process also leads to an obligate codependency. The relocated genes control the division of the organelles (synchronization) and encode products that interact with organelle-encoded proteins. In turn, the genes still present in the organellar genome encode proteins that interact with nuclear proteins [108]. Ultimately, the organelle interacts with its own evolved genes physically present in the nucleus of the cell. Nevertheless, some of these DNA containing organelles still are organisms in their own right; genetically equipped for the environment imposed by the cytoplasm of the host cell. Intracellular signaling pathways that coordinate gene expression between organellar and nuclear genomes are highly complex; toward almost complicated [109]. Moreover, additional signaling pathways exist between different organellar genomes [109]. These complications may be one of the reasons for the reductive evolution of the organellar genomes. However, many organelles retained a large part from their ancestral genome. Thus, different equilibrium states between organellar and nuclear genomes must exist. Moreover, contrary to certain sedimented expectations, prokaryotic organisms also may contain organelles with special arrangements; for instance organelles such as magnetosomes, chlorosomes, pirellulosomes, anammoxosomes, carboxysomes, and so on [110–112].