A Kunz — Page 3 | PubMed Health

PubMedDate not supplied

An experimental selection system to identify bacterial cells exhibiting a new DNA host specificity.

Restriction-modification enzymes interact with DNA sequences in a highly specific manner. Mutations within the DNA binding region of the enzymes could be expected to produce enzyme variants with changed DNA sequence specificities. We developed an efficient in vivo selection system that enabled us to detect one cell coding for a restriction-modification system with a new DNA sequence specificity in a background of more than 10(6) cells with the original DNA sequence specificity.

Bacteriophage lambda↗

PubMedDate not supplied

Mutual activation of two restriction endonucleases: interaction of EcoP1 and EcoP15.

Type III restriction endonucleases recognize nonsymmetric nucleotide sequences. A necessary condition for DNA cleavage is the presence of two unmethylated recognition sites which are inversely ('head-to-head') oriented in the DNA double strand. A DNA substrate possessing one EcoP1 and one EcoP15 site in the head-to-head configuration could not be cleaved by the individual enzymes, however, it was specifically digested in the simultaneous presence of both enzymes. In agreement with the tracking-collision model for the DNA interaction of type III enzymes cleavage could be abolished by Lac repressor bound between the two sites. We conclude that two different type III enzymes can functionally cooperate in the cleavage of DNA.

DNA Methylation↗