Antisense RNA mediates transcriptional processing in an archaebacterium, indicating a novel kind of RNase activity.

Strains of the extremely halophilic archaebacterium Halobacterium salinarium that are lysogenic for the phage phi H produce an antisense RNA transcript complementary to the first 151 nucleotides (nt) of the early lytic phage transcript T1. This is the first case of antisense control of gene expression in an archaebacterium. We show through transformation of H. salinarium that the antisense RNA functions in trans, rendering the early lytic phage transcript T1 susceptible to specific cleavage by an unidentified RNase of unique endonucleolytic activity. The single-stranded ends of RNA are cut off at the ends of the 151 nt RNA duplex, removing the ribosomal binding sites from the first open reading frame of transcript T1 but without concomitant digestion of the products.