Biomedical subjects

S D Hesse

Publications and source records attributed to S D Hesse.

3 recordsLinked to original sources

PubMed1986

Mutational analysis of integrase arm-type binding sites of bacteriophage lambda. Integration and excision involve distinct interactions of integrase with arm-type sites.

Integrative recombination between specific attachment (att) regions of the bacteriophage lambda genome (attP) and the Escherichia coli genome (attB) results in a prophage flanked by the hybrid recombinant sites attL and attR. Each att site contains sequences to which proteins involved in recombination bind. Using site-directed mutagenesis, we have constructed a related set of point mutations within each of the five Int "arm-type" binding sites located within attP, attL and attR. Footprint analyses of binding demonstrate that mutating the arm-type sites significantly disrupts the binding of Int. Recombination analyses of mutant att sites in vivo and in vitro demonstrate that only three wild-type arm-type sites within attP are required for efficient integrative recombination. Similar analyses demonstrate that efficient excision can occur with two other different sets of wild-type arm-type sites in attL and attR. These results demonstrate that integrative and excisive recombination may involve interactions of Int with distinct and different subsets of arm-type sites.

Attachment Sites, Microbiological↗

PubMed1985

A genetic enrichment for mutations constructed by oligodeoxynucleotide-directed mutagenesis.

A genetic enrichment procedure for mutations constructed by oligodeoxynucleotide(oligo)-directed mutagenesis of DNA cloned in M13mp vectors is described. The procedure uses an M13 vector that contains the cloned target DNA and amber (am) mutations within the phage genes I and II. This vector cannot replicate in a suppressor-free (sup degrees) bacterial strain. A gapped heteroduplex is formed by annealing portions of a complementary (-)strand containing wild-type copies of genes I and II to the am-containing template (+)strand. The oligo is annealed to the single-stranded (ss) region and the remaining gaps and nicks are repaired enzymatically to form a closed circular heteroduplex structure. By transfecting the DNA into a sup degrees host we promote the propagation of heteroduplexes with the oligo-containing (-)strand since only this construction contains the wild-type copies of genes I and II. This procedure eliminates the need for any physical separation of the covalently closed circular DNA that contains the oligo from the ss template. Using this technique we have constructed 17 point mutations with mutation frequencies ranging from 2-20% for single base changes and from 0.3-9% for multiple base changes. In addition, we found that the mutation frequencies were affected by the state of DNA methylation in the (+) and (-)strands.

Coliphages↗

PubMed1984

DNA interactions during bacteriophage lambda site-specific recombination.

Extensive research on site-specific recombination has provided many details, particularly with respect to the protein-DNA interactions. However, very little is known about the molecular mechanism of recombination during synapsis and strand exchange. Presumably, these steps of recombination involve various forms of DNA-DNA, DNA-protein, and protein-protein interactions. One stage at which DNA-DNA interactions may be occurring is at the level of synapsis where the recombining DNAs are juxtaposed. In this paper we have presented evidence that homology-dependent DNA interactions do occur within the overlap region before strand exchange. This interaction is presumably at the synaptic stage of recombination. Furthermore, we have demonstrated that the homology-dependent interactions require that only one strand of attB have homology to attP. Another stage in recombination at which DNA-DNA interactions could occur is during strand exchange where complementary strands from the recombining parents are paired and resealed. We have also presented evidence that homology-dependent DNA interactions occur during strand exchange prior to the resealing of the strands and that disruption of this interaction results in nonreciprocal recombination. Taken together, these results suggest that DNA-DNA interactions during reciprocal site-specific recombination occur during at least two stages in the reaction.

Bacteriophage lambda↗