Deoxyribonucleic Acid Sequence Homologies Among Bacterial Insertion Sequence Elements and Genomes of Various Organisms

Plasmid and phage deoxyribonucleic acid (DNA) harboring bacterial insertion sequence (IS) elements IS1 , IS2 , and IS5 were characterized and used as probes to detect homologous sequences in various procaryotic and eucaryotic genomes. The hybridization method used permits the detection of sequences partially homologous to the elements. Hybridization of the IS-containing probes to each other revealed a region of limited homology between IS1 and IS2 . Homologous sequences were then detected by computer analysis of the published IS1 and IS2 nucleotide sequences. The homologous sequence contains a tandemly repeated tetranucleotide sequence which resembles the repeated sequence at the hot spot for spontaneous mutations in thelacI gene (P. J. Farabaugh, U. Schmeissner, M. Hofer, and J. Miller, J. Mol. Biol.126: 847–863, 1978). Homology between the IS elements and various genomes was determined by hybridizing labeled DNA containing IS1 , IS2 , and IS5 sequences to Southern blots of chromosomal DNA cleaved with restriction endonucleases. IS1 and IS5 appear limited to the enteric bacteria, whereas IS2 sequences can also be detected inPseudomonas putida, Pseudomonas aeruginosa , andSerratia marcescens . Bacteria which appear not to possess extrachromosomal elements, e.g.,Caulobacter crescentus , did not show homology with any insertion sequences tested. In addition, sequences homologous to IS1 , IS2 , or IS5 were not detected inSaccharomyces cerevisiae, Dictyostelium discoideum , or calf thymus DNA.