Conclusion Figure 3. Unusual long palindromic GI, GII and GIII sequences and their potential evolution from REP doublets found in the SBW25 genome. (A) Shown are all four long palindromic GI, GII and GIII sequences together with their frequency found in the SBW25 genome. Note that two configurations are found for GI sequences and only one for both GII and GIII sequences. (B) Shows how long palindromic REP singlets could arise from REP doublets ©doublets 2found in 0TT-AA 1orienta2tionbc-palinLdromea-bREPs n(right)d. through the excision of the central sequence. Hence, REP doublets found in AA-TT orientation would produce a-palindrome-ac REPs (left) and REP es Bioscience. the REPIN-RAYT association, along with light on regulation of REPIN movement knowledge of the functional significance and with this there might emerge possibilities REPINs and their associated RAYTs are a of the interaction for the host cell. From for controlling microbial infection through as indicated here, there Dismuch oabout tnheir otoknotwwhedther REiPIsNsaretderrived ifrobmute. common feature of bacterial genomes, yet an evolutionary perspective it is of interest manipulation of selfish element behavior. Acknowledgments origin, maintenance and means of dissem- REP sequences flanking ancestral IS200- ination (both with and between genomes) like elements as has been suggested. Also FB acknowledges a post-graduate scholar- that is currently unknown. Critical for progress are studies that shed light on the of mechanism RAYT-mediated REPIN mobilization and the basis of worthy of study are the dynamics of REPIN movement along with the spec- trum of mutational effects wrought by transposition. Future work may even shed ship from the Allan Wilson Centre; PBR is supported by a James Cook Research Fellowship from the Royal Society of New Zealand. Figure 4. Incomplete symmetric excision event of a REP doublet detected in Illumina sequencing data. The first line of the alignment shows the genomic sequence of SBW25 from position 598,553 to position 598,634. The second line of the alignment shows part of the sequence read that maps perfectly to the corresponding genome sequence apart from the excision in the center of the read. The cartoon below the alignment shows the general composition of the GI REP doublet. The last line in the picture shows the remaining REP sequence found in the sequence read. It only contains flanking sequence (a), the central palindrome and flanking sequence (ac). www.landesbioscience.com Mobile Genetic Elements 267