A transposable element from Halobacterium halobium which inactivates the bacteriorhodopsin gene.

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Abstract
The characterization of a transposable element from an archaebacterium is described. The bacteriorhodopsin genes from the wild-type and 2 mutant H. halobium strains were cloned as BamHI fragments in plasmid pBR322. The cloned DNA fragments from the 2 mutants both contain a 1.1-kilobase-pair insertion sequence (ISH1) near the NH2 terminus of the bacteriorhodopsin coding sequence. ISH1 is present in the 2 mutants in an identical palindromic site but in opposite orientations. The complete sequence of ISH1 was determined; it is 1118 nucleotides long, it has 8-base-pair interrupted inverted repeats at the ends, and it duplicates an 8-base-pair (A-G-T-T-A-T-T-G) target sequence upon insertion. As for most eukaryotic and some prokaryotic transposable elements, the sequence of the ISH1 begins with T-G and ends in C-A. ISH1 contains an open reading frame 810 nucleotides long and codes for an RNA .apprx. 900 nucleotides long. The copy number of ISH1 ranges from 1-5 or more in different H. halobium strains. In at least one of the strains, 1 copy of ISH1 is present also on a plasmid DNA.