Abstract
We have investigated the effect of the polyamines spermine, spermidine, and putrescine and the prokaryotic histone-like proteins NS1 and NS2 on the restriction endonuclease EcoRI catalyzed cleavage of plasmid and bacteriophage DNAs. At low concentrations of spermine and spermidine, the rate of DNA cleavage by EcoRI is increased, while high concentrations of spermine as well as of spermidine are inhibitory. These phenomena are also observed with other restriction endonucleases. They are, therefore, probably due to the interaction of the polyamines with the DNA. Putrescine does not have such an effect within the concentration range investigated. Remarkably, low concentrations of spermine and spermidine very efficiently suppress EcoRI activity. An inhibition of the EcoRI-catalyzed cleavage of DNA is also observed with NS1 and NS2, an effect that can be mimicked with other basic proteins that interact with DNA. The results are discussed in terms of the mechanism of restriction in vivo.
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