Reversible Molecular Computation in Ciliates
نویسندگان
چکیده
We prove that a reversible model for the guided homologous recom-binations that take place during gene rearrangement in ciliates has the computational power of a Turing machine, the accepted formal model of computation. This indicates that, in principle, these unicellular organisms may have the capacity to perform any computation carried out by an electronic computer. 1 Gene unscrambling as computation Ciliates are a diverse group of 8000 or more unicellular eukaryotes (nucleated cells) named for their wisp-like covering of cilia. They possess two types of nuclei: an active macronucleus (soma) and a functionally inert micronucleus (germline) which contributes only to sexual reproduction. The somatically active macronucleus forms from the germline micronucleus after sexual reproduction , during the course of development. The genomic copies of some protein-coding genes in the micronucleus of hypotrichous ciliates are obscured by the presence of intervening non-protein-coding DNA sequence elements (internally eliminated sequences, or IESs). These must be removed before the assembly of a functional copy of the gene in the somatic macronucleus. Furthermore, the protein-coding DNA segments (macronuclear destined sequences, or MDSs) in species of Oxytricha and Stylonychia are sometimes present in a permuted order relative to their nal position in the macronuclear copy. For example, in O. nova, the micronuclear copy of three genes (Actin I,-telomere binding protein, and DNA polymerase) must be reordered and intervening DNA sequences removed in order to construct functional macronuclear genes. Most impressively, the gene encoding DNA polymerase (DNA pol) in O. trifallax
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