The isolation of IS1 and IS2 DNA

Transactivation of several genes of two native Serratia prophages after superinfection by phage kappa

Serratia marcescens HY bacteria must be lysogenic with either prophage y or psi to make it possible for phage kappa to form plaques unless they carry a so-called ink mutation. Genes in y and psi termed any and anp were identified that after infection of ink+ cells are necessary for an effective propagation of these phages as well as of coinfecting kappa phage. When kappa infects y and/or psi-lysogenic cells it transactivates the respective prophage genes by means of two early genes termed tay and tap. It appears that on infection of nonlysogenic ink+ cells kappa damps its own development, provided the regulatory region of the responsible gene is undermethylated. After kappa infection duly to achieve the special methylation of this region seems to be the function of any and anp. There are some more genes in y and psi prophage under the control of tay and tap, concerning in both cases a Dam methylation (recognition sequence GATC) of kappa DNA, a recombination proneness under restricting conditions of kappa DNA not modified by the modification enzyme of HY, and the kappa plaque size. By hybridization studies a region of homology common to y and psi was demonstrated which from its size might comprise all the transactivated genes. The view is supported by genetic data indicating an affinity among the any and anp genes. Investigation of various any mutants were indicative of DNA inversions in this region of the y genome. Surprisingly some of the any mutants had become sensitive in their plaque forming ability to an inhibitory activity exerted by prophage psi. Mutants of psi unable to interfere but still able to lysogenize were isolated. A model is presented accounting for the formation of pleiotropic and nonpleiotropic mutations with Any phenotype and their reversion types. Possible functions of the y genes and their counterparts in psi are discussed.

IS4 at its chromosomal site in E. coli K12

IS4 DNA has been isolated in pure form. Hybridization of this DNA against restricted DNA of several E. coli K12 strains by Southern's blotting technique has shown that, in most strains, only one copy of IS4 is present. Though the restriction fragments around this site differ in size, IS4 can be shown always to be located at the same site. In one strain, one additional copy has been found in a new location. In this strain, IS4 in its original location has been retained.

Cloning and endonuclease restriction analysis of argF and of the control region of the argECBH bipolar operon in Escherichia coli

A 1.8 kb DNA fragment, liberated by endonuclease HindIII, contains the control region of the argECBH bipolar operon near one end and the weak secondary promoter of argH at the other extremity; it has been cloned in plasmid pBR322. The same plasmid vector has been used to clone the argF gene liberated from the chromosome by endonuclease BamHI. Restriction patterns for the two hybrid plasmids have been determined, using enzymes AluI, BglI, EcoRI, HaeIII, HincII, HindIII, HpaI and II, PstI and SalI. Two AluI sites situated on either side of and close to a HincII target delineate two short fragments covering the whole of the argECBH control region. The argF control elements are located in a region accessible to further dissection by BamHI, EcoRI, PstI and HindIII. Carriers of the argF plasmid produce extremely high amounts of ornithine carbamoyltransferase, a feature useful for purification of this enzyme.

Involvement of IS1 in the dissociation of the r-determinant and RTF components of the plasmid R100.1

The formation of the r-determinant pLC1 and of the RTF pAR132 from the composite plasmid R100.1 was investigated. The general location of IS1 sequences on the three plasmids was established by hybridization of lambdar14 CII::IS1 DNA to EcoRI generated fragments of the various plasmids separated by agarose gel electrophoresis and transferred directly to nitrocellulose filters. The position of IS1 sequences on these fragments and the homologies between fragments were analyzed by electron microscopy of heteroduplex molecules. The results show that the excision of both pLC1 and pAR132 occurred by an exchange between the two IS1 sequences present on R100.1.

Transcription of insertion elements IS1 and IS2 in vitro

Insertion elements IS1 and IS2 integrated within the gal operator-promoter region, an IS1 element in gene galT and insertions IS1 and IS2 integrated in the xycIIOP region of phage lambda were transcribed in vitro with E. coli RNA-polymerase. The insertion elements are transcribed exclusively by polymerase molecules started at the gal promoter and the lambdaPR promoter respectively. No promoter exists on IS1 or IS2 which can be recognized by RNA-polymerase in the pure in vitro transcription system used. Both insertions apparently are transcribed with a lower elongation rate than gal operon DNA or lambdaDNA. RNAs transcribed from the termini of IS1 and IS2 respectively were analysed by hybridization experiments. They are different in sequence.