A reverse transcriptase enzyme and genomic repeat sequences coordinate a tropic switch in a bacteriophage.
Certain Bordetella bacteria exist in two phases – Bvg+ is characterized by the expression of virulence genes and respiratory tract colonization, while the Bvg- phase is adapted for ex vivo growth when virulence genes are silenced. In the March 15 Science Minghsun Liu and colleagues from the University of California in Los Angeles, describe how bacteriophages target specific bacterial phases (Science 2002, 295:2091-2094).
Liu et al. found that the bacteriophage BPP-1 (Bvg plus tropic phage-1) had a tropism for the Bvg+ phase bacteria. They identified the prn gene, encoding the adhesin pertactin, as essential for tropism, and were able to isolate bacteriophage variants with different tropisms, implying a mechanism of tropic switching. They then looked at tropic variants and noticed a 134 bp repeat sequence within the mtd (major tropism determinant) locus, which is repeated in an adjacent brt locus encoding a Bordetella reverse transcriptase enzyme....
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