Irradiation-Induced Deinococcus radiodurans Genome Fragmentation Triggers Transposition of a Single Resident Insertion Sequence

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.

Single-Stranded DNA Transposition Is Coupled to Host Replication

“…It has a similar organisation to IS 608 and inserts specifically 3' to a TTGAT pentanucleotide (Islam et al, 2003). Like IS 608 , it transposes using ssDNA intermediates (Pasternak et al, 2010). We had observed specific stimulation of IS Dra2 transposition upon γ- or UV-irradiation (Mennecier et al, 2006; Pasternak et al, 2010) related to the availability of ssDNA generated during radiation-induced fragmentation and reassembly of the host genome, called extended synthesis dependent strand annealing (ESDSA; Zahradka et al, 2006).…”

“…D. radiodurans replication is thought to be bidirectional (Hendrickson and Lawrence, 2006). We constructed D. radiodurans strains with an IS Dra2 derivative, IS Dra2 -113 (Pasternak et al, 2010), placed in one or the other orientation at the same chromosomal location (Supplementary Experimental Procedures). Excision of these ISs reconstitutes a functional Tc R gene.…”

Oxidative Stress Resistance inDeinococcus radiodurans

“…One of the IS elements, ISDra2 (IS200/IS605 family), is present at different copy numbers in different D. radiodurans strains (14,270,381). Whereas the level of ISDra2 transposition is very low in the absence of stress, it is highly induced in irradiated cells (408,484). Single-stranded DNA intermediates formed during postirradiation genome reconstitution (see "Recombinational Processes in D. radiodurans DNA Repair") favor the transposition of ISDra2, the excision of which proceeds via a single-stranded DNA circle (484).…”

“…Whereas the level of ISDra2 transposition is very low in the absence of stress, it is highly induced in irradiated cells (408,484). Single-stranded DNA intermediates formed during postirradiation genome reconstitution (see "Recombinational Processes in D. radiodurans DNA Repair") favor the transposition of ISDra2, the excision of which proceeds via a single-stranded DNA circle (484). Another IS family, ISDra5, is responsible for the translocation of the small plasmid into the large chromosome, which occurs spontaneously in the recA mutant cells and after high doses of ionizing radiation in wild-type cells (514) (see "Fidelity of DNA Repair in Irradiated D. radiodurans").…”

Sense overlapping transcripts in IS1341-type transposase genes are functional non-coding RNAs in archaea

“…15,16 The mechanism of transposition is unique among IS elements since it requires single stranded DNA as substrates. 15,17 The tnpB gene is not required for transposition 14,18 , however, it is known to play a regulatory role by inhibiting excision and insertion of ISDra2 in Deinococcus radiodurans. 19 Mechanisms of TnpB action are currently unknown.…”