Isolation, sequence, and expression of the gene encoding halocin H4, a bacteriocin from the halophilic archaeon Haloferax mediterranei R4

The first gene to encode a haloarchaeal bacteriocin (halocin H4) has been cloned and sequenced from Haloferax mediterranei R4. Both the signal sequence in the halocin H4 preprotein and the monocistronic halH4 gene have some unusual features. The physiology of halH4 expression reveals that although halH4 transcripts are present at low basal levels during exponential growth, halocin H4 activity first appears as the culture enters stationary phase. As halocin activity levels increase, so do transcript levels, but then activity levels decrease precipitously while transcript levels remain elevated.