Journal
JOURNAL OF THEORETICAL BIOLOGY
Volume 229, Issue 3, Pages 361-369Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jtbi.2004.04.001
Keywords
adaptive mutations; cAMP; cell differentiation; DNA supercoiling; critical period; nonlinear dynamics; phase transition; genome modifications; Lamarckian evolution
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Adaptive changes in bacteria are generally considered to result from random Mutations selected by the environment. This interpretation is challenged by the non-randomness of genomic changes observed following ageing or starvation in bacterial colonies. A theory of adaptive targeting of sequences for enzymes involved in DNA transactions is proposed here. It is assumed that the sudden leakage of cAMP consecutive to starvation induces a rapid drop in the ATP/ADP ratio that inactivates the homeostasis in control of the level of DNA supercoiling. This phase change enables the emergence of local modifications in chromosome topology in relation to the missing metabolites, a first stage in expression of an adaptive status in which DNA transactions are induced. The nonlinear perspective proposed here is homologous to that already suggested for adaptation of pluricellular organisms during their development. In both cases, phases of robustness in regulation networks for genetic expression are interspaced by critical periods of breakdown of the homeostatic regulations during which, through isolation of nodes from a whole network, specific changes with adaptive value may locally occur. (C)2004 Elsevier Ltd. All rights reserved.
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