Nucleotide-sequence Analysis of Tn3 (Ap): Implications for Insertion and Deletion

Abstract

IS elements are segments of DNA which occur in several size classes (700–1400 bp) and appear as insertion mutations in various operons (Hirsch et al. 1972; Fiandt et al. 1972; Chow and Broker 1978). These elements are present as repeated sequences in bacterial plasmids including the fertility factor, F, and the resistance factor, R, and in the bacterial chromosome (Hu et al. 1975a,b; Ohtsubo and Ohtsubo 1977a; Saedler and Heiss 1973). Insertion of an IS element into an operon causes strong polarity due to interference at the level of transcription (Starlinger et al. 1973; Saedler et al. 1974; Adhya et al. 1976). Excision of this element restores normal function of the operon (Saedler and Starlinger 1967). In this way IS elements can control gene expression.