DNA base sequence is not the only factor for restriction endonuclease activity on metaphase chromosomes: evidence using isoschizomers.

Human and mouse fixed metaphase chromosomes were treated with the isoschizomer sets MboI/Sau3A and EcoRII/BstNI. In both cases we found that each member of the isoschizomer pairs produced different results, indicating that factors other than DNA base composition may affect in situ digestion by restriction endonucleases and that the structure of the enzymes is one factor. We also found that MboI and Sau3A isoschizomers produced the same effect on the chromosomes of the grasshopper Oedipoda germanica. This indicated that differences in the chromatin structure of different species may be important in determining restriction endonuclease activity on eukaryotic chromosomes.