Insertion elements and deletion formation in a halophilic archaebacterium

Abstract

Deletion events that occur spontaneously in 36-kilobase-pair (kbp) plasmid pHH4 from the archaebacterium Halobacterium halobium were investigated. Four different deletion derivatives with sizes ranging from 5.7 to 17 kbp were isolated. Three of these deletion variants derived from pHH4 (pHH6 [17 kbp], pHH7 [16 kbpJ, and pHH8 [6.3 kbpJ), whereas the 5.7-kbp plasmid pHH9 derived from pHH6. Strains containing pHH6, pHH7, or pHH9 each lacked the parental plasmid pHH4, while pHH8 occurred at a 1:1 ratio together with p4H4. Common to all of these plasmids was the 5.7-kbp region of pHH9 DNA. The regions containing the fusion site in the deletion derivatives were investigated and compared with the corresponding area of the parental plasmid. Each deletion occurred exactly at the terminus of an insertion element. In pHH6 and pHH7, a halobacterial insertion element (ISH2) was located at the deletion site. The DNA fused to ISH2 displayed a 7-base-pair (bp) (pHH7) or 10-bp (pHH6) sequence homology to the inverted repeat of ISH2. In the two smaller plasmids, pHH8 and pHH9, an ISH27 element was located at the deletion site. Most likely, all of these smaller plasmids resulted from an intramolecular transposition event. The ISH27 insertion sequence contains a 16-bp terminal inverted repeat and duplicates 5 bp of target DNA during the transposition with the specificity 5'ANNNT3'. Four ISH27 copies were analyzed, and two ISH27 element types were identified that have approximately 85% sequence similarity. The ISH27 insertion elements constitute a family which is related to the ISH51 family characterized for H. volcanii, another halophilic archaebacterium.

Transcript analysis of the c-vac region and differential synthesis of the two regulatory gas vesicle proteins GvpD and GvpE in Halobacterium salinarium PHH4

“…The wild-type strain H. salinarium PHH1 contains the two vac regions p-vac and c-vac, but only the p-vac region is expressed and leads to the synthesis of spindle-shaped gas vesicles throughout the growth cycle. The c-vac region is expressed only when the p-vac region is deleted, as has been found for H. salinarium PHH4 carrying plasmid pHH4, which is a 35-kb deletion variant of plasmid pHH1 (15,21). In contrast to the spindle-shaped gas vesicles of wild-type H. salinarium PHH1, c-vac-encoded gas vesicles are cylindrical and appear only in the stationary growth phase.…”

Use of a halobacterial bgaH reporter gene to analyse the regulation of gene expression in halophilic archaea

“…The c-vac region is expressed only in p-vac deletion strains such as Hb. salinarum PHH4 harbouring the 35 kb plasmid pHH4 (Pfeifer & Blaseio, 1989).…”

Conservation of chromosomal arrangement among three strains of the genetically unstable archaeon Halobacterium salinarium

“…The ability to form gas vesicles, encoded by the gyp operon, is lost at an even higher rate of about 10-2. The Gvp-phenotype results from two types of events: duplicative transpositions of ISH and deletion events consistent with abortive intramolecular transposition (3,9,10).…”

“…The hypermutable gyp operon and most copies of the ISH are in the plasmid fraction, which is also consistent with the model. In H. salinarium, all characterized mutations are mediated by ISH elements (1,3,(8)(9)(10).…”