STUDIES ON THE BACTERIOPHAGE-MS2 .38. IDENTIFICATION OF THE TRANSLOCATABLE ELEMENT IS1 IN A MOLECULAR CHIMERA CONSTRUCTED WITH PLASMID PARA-BR322 DNA INTO WHICH A BACTERIOPHAGE-MS2 DNA COPY WAS INSERTED BY THE POLY(DA).POLY(DT) LINKER METHOD

Analysis of the plasmic DNA derived from a colony of bacteria [Escherichia coli] carrying pMS2-7 [plasmid with full-length MS2 DNA insertion] revealed the presence of an additional, smaller plasmid DNA, identified as pMS2-701. pMS2-701 also contained the nearly full-length MS2 DNA copy, but the extra DNA insertion present to the right of the MS2 DNA insert in pMS2-7 was absent. Transformation of E. coli with a DNA preparation containing both plasmid DNA allowed the recloning of the pMS2-701 plasmid. Upon further subculturing the pMS2-7 type plasmid containing the extra DNA insertion reappeared. The proportion of pMS2-7 relative to pMS2-701 increased in the course of successive subcultures. The extra DNA insertion in pMS2-7 was identified as the translocatable element IS[insertion sequence]1 by mapping of restriction sites and by nucleotide sequence analysis. The boundaries between IS1 and pMS2-7 DNA revealed that IS1 was inserted between the N[amino]-proximal part of the ampicillin gene and the poly(dA) .cntdot. poly(dT) linker, and that a repetitious sequence of 9 base-pairs in length was generated by the translocation process.