[Distribution of DNA sequences recognized by specific endonucleases]

The molecular weight distributions of fragments obtained after endonuclease treatment of DNA were studied. DNA's from pigeon and E. coli and restriction enzymes EcoRI and BamHI were used. The samples of 14C- and 3H-labelled DNA were treated by endonucleases, separated electrophoretically in 1% agatose gels, and radioactivity distributions along gels were measured. From these data weight and number distributions and the average molecular weights of DNA fragments were determined. EcoRI-fragments of phage DNA were used as standards for the molecular weight calibration. The experimental results are compared with the expected data calculated from the DNA GC content. The molecular weight distribution of fragments and the average molecular weights of BamHI-fragments of pigeon DNA and EcoRI- and BamHI-fragments of E. coli DNA differed from random ones. It is suggested that certain genomes contain regions in which the probability of endonuclease cleavage strongly differs from the average probability of such a cleavage for the entire genome.