E. coli ribosomal RNA contains sequences homologous to insertion sequences IS1 and IS2

The insertion sequence (IS) elements, IS1 and IS2, present in multiple copies in the Escherichia coli chromosome, are transposable genetic elements of known nucleotide sequence. These elements can modulate gene expression, but it is not known whether they normally function in genetic control. To determine whether IS elements could exert control through specific RNA transcripts, we hybridised lambda NNC1857 r14 (carrying IS1) and pBR322 (carrying a portion of IS2) to Northern blots of E. coli RNA. Regions of homology between the IS elements and ribosomal RNA were observed. Computer analysis of reported nucleotide sequences detected large segments of homology between the IS elements and both 23S and 16S rRNA. Additional homologous sequences in phi X174 and a leader region of a ribosomal protein gene cluster were also detected. The homologous sequence between IS2 and 16S rTNA is the same sequence in phi X174 DNA which codes for the ends of the E and D gene and the start of J. The partial IS sequences may represent silent evolutionary remnants or they could modulate the expression of genes carrying these sequences.