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Germ Line DNA Parasites That Have Converged on an Altruistic Somatic Excision Strategy, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555816810/9781555815387_Chap31-1.gif /docserver/preview/fulltext/10.1128/9781555816810/9781555815387_Chap31-2.gifAbstract:
This chapter discusses certain DNA elements that parasitize organisms that have evolved a germ line-soma developmental strategy. By way of introducing the main ideas of this essay, the author briefly summarizes the strategy of the somatic excision element (SEE) called skin that interrupts the sigma K gene of many endospore-forming bacteria, discovered first in Bacillus subtilis. Finally, the author draws analogies to introns and inteins. Division-of-labor germ line-soma strategies, analogous to that employed by metazoans, have evolved independently in numerous other life forms; that is, these life forms have convergently evolved germ line-soma strategies. An elaborate germ line-soma developmental program is employed by ciliated protozoa with the germ line carried in the transcriptionally silent micronucleus, coresident in the cell with the somatic or macronucleus, its DNA pure genes, and it a specialized organelle for expressing them. Both spliceosomal introns and inteins appear to have been inserted into genes as mobile elements, the former derived from transposed group II self-splicing introns and the latter as representatives of mobile homing endonuclease genes. Both introns and inteins are DNA segments interrupting genes. Given the widening horizon that genomic sequencing affords and the large number of unexplored germ line-soma systems, the author imagines that many may have become infested with SEEs.