Transposition burst of the ISH27 insertion element family inHalobacterium halobium

Abstract

Investigation of the plasmid pHH4 in single colonies of Halobacterium halobium PHH4 indicated transposition of insertion elements in 20% of the colonies. Seven ISH27 insertions were observed as well as one ISH23 insertion. The various copies of ISH27 were compared to the two ISH27 elements already present in pHH4, and to the ISH27 element that was identified in the bacteriopsin (bop) gene of a Bop mutant. These ten copies of ISH27 constitute three types on the basis of DNA sequence identity: ISH27-1 (1398 bp), ISH27-2, and ISH27-3 (1389 bp each). The DNA sequence comparison between the three types indicates a region of 1200 bp where the identity between ISH27-1 and ISH27-2 or ISH27-3 is 82-83%. ISH27-2 and ISH27-3 are 95% identical in this region. The remaining region exhibits a lower DNA similarity (64-74% identity) between the different copies. An open reading frame of 1167 nucleotides spans the more conserved region, and a corresponding transcript could be detected in H. halobium PHH4, but not in H. halobium wild-type. ISH27-1 is 91% identical to members of the insertion sequence-like elements ISH51 of Haloferax volcanii, whereas the other two ISH27 element types are 82-83% identical to ISH51. The transposition 'burst' of ISH27 was only seen after storage of the cells for more than two years at 4 degrees C. Upon continuous cultivation at 37 degrees C no transposition event could be observed, suggesting that stress factor(s) might have caused the high transposition rate.

Genetic reductionist approach for dissecting individual roles of GGDEF proteins within the c-di-GMP signaling network in Salmonella

“…However, a c-di-GMP component that controls this process also exists, because the individual presence of AdrA or HmsT in ⌬XII blocked motility in a manner that depended on the presence of an active GGDEF site. The latter finding is in agreement with previous studies that correlate high levels of c-di-GMP and sessility (12,(35)(36)(37)(38).…”

Genomic demography: a life-history analysis of transposable element evolution

“…In reality, transposable elements are thought to undergo bursts of transposition followed by periods of stasis (see, for example, Georgiev et al 1989;Gerasimova et al 1984;Pfeifer & Blaseio 1990). Thus, in a second model, we assume that the initial infection by a single element was followed by a rapid burst of transposition, giving rise to the present number of elements in a few tens of generations.…”

Directed mutation: between unicorns and goats

“…Indeed, increased movement of insertion elements during stationary phase has previously been observed (3,30,45) and could be related to changes in DNA topology that occur in starving cells (39). What factor actually triggers excision might depend on how the cells entered into stationary phase.…”