AN INTERVENING SEQUENCE (IVS) IN THE 16S RIBOSOMAL-RNA GENE OF THE EUBACTERIUM HELICOBACTER-CANIS

PCR amplicons enlarged by similar to 250bp were generated from the 16S rRNA (rrs) genes of certain strains of the recently described Helicob acter species, H.canis. The DNA sequence of the rrs gene of one such s train was determined, and it was shown that an intervening sequence (I VS) of 235bp followed nucleotide 199 in the rrs sequence. In four othe r H.canis strains, identical or similar IVSs were found, always at the same location in the rrs gene. The secondary structures of the RNA tr anscripts of the IVSs were predicted. They were characterised by the p resence of a conserved stem-loop structure, a potential recognition si te for RNA processing enzymes. Ribosomal RNA was compared from a strai n of H.canis with and without the IVS-containing rrs gene. In the form er 16S rRNA appeared as two fragments, whose sizes were consistent wit h cleavage at either side of the IVS, and which were not subsequently religated. The IVS sequence was not represented elsewhere in the H.can is genome. Its evolutionary significance is discussed.