Abstract
Stress-induced transposition is an attractive notion since it is potentially important in creating diversity to facilitate adaptation of the host to severe environmental conditions. One common major stress is radiation-induced DNA damage. Deinococcus radiodurans has an exceptional ability to withstand the lethal effects of DNA–damaging agents (ionizing radiation, UV light, and desiccation). High radiation levels result in genome fragmentation and reassembly in a process which generates significant amounts of single-stranded DNA. This capacity of D. radiodurans to withstand irradiation raises important questions concerning its response to radiation-induced mutagenic lesions. A recent study analyzed the mutational profile in the thyA gene following irradiation. The majority of thyA mutants resulted from transposition of one particular Insertion Sequence (IS), ISDra2, of the many different ISs in the D. radiodurans genome. ISDra2 is a member of a newly recognised class of ISs, the IS200/IS605 family of insertion sequences.
Highlights
Stress-induced transposition has been an attractive notion for some time since it is potentially important in creating diversity to facilitate adaptation of the host to severe environmental conditions
In Deinococcus radiodurans, the most radiation-resistant organism known, despite abundance of resident insertion sequences (IS), transposition of a single Insertion Sequence (IS), ISDra2, was found to be strongly induced by irradiation. We show that both steps involved in transposition, IS excision, and insertion, increase significantly following host cell irradiation and, using PCR analysis of genomic DNA, that exposure to c-irradiation stimulates massive excision of the single genomic ISDra2 copy as a DNA circle and reclosure of the empty site
Consistent with this, we demonstrate a requirement for single strand DNA substrates in TnpA-catalysed cleavage and strand transfer in vitro
Summary
Stress-induced transposition has been an attractive notion for some time since it is potentially important in creating diversity to facilitate adaptation of the host to severe environmental conditions. One common major stress is DNA damage This induces a variety of responses including changes in expression of numerous genes [1,2,3,4], cell cycle arrest [5,6], induction of bacterial prophages [7,8] and, by generating diversity, can aid development of processes such as bacterial pathogenicity and virulence [9]. Several studies have focused on DNA damage-induced transposition in bacteria but have not yet provided a coherent mechanistic scenario. This interest presumably stemmed directly from capacity of UV-irradiation to promote lysogenic induction [7]. We identify and demonstrate the molecular basis of a strong radiationstimulated response of transposition in the irradiation resistant Deinococcus radiodurans
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