Mutation Research, 150 (1985) 359-368 359 Elsevier MTR 02041 Chromosomal aberrations induced by restriction endonucleases G. Obe 1,2, F. Palitti 3, C. Tanzarella 2, F. Degrassi 3 and R. De Salvia 3 t lnstitut fftr Genetik, Freie Unioersit~t Berlin, A rnimallee 5-7, D- 1000 Berlin 33 (F.R.G.), 2 Dipartimento di Genetica e Biologia Molecolare, Citth Universitaria Roma, Piazza& Aldo Moro 5, 1 00185 Roma (Italy) and 3 Centro Genetica Evoluzionistica C.N.R., c/o Dipartimento di Genetica e Biologia Molecolare, Citth Universitaria Roma, Piazzale Aldo Moro 5, 1 00185 Roma (Italy) (Received 30 November 1984) (Revision received 6 February 1985) (Accepted 8 February 1985) Summary Restriction endonucleases (REs) are able to induce chromosomal aberrations in Chinese hamster ovary (CHO) cells. The G1 phase of the cell cycle seems to be especially sensitive for the induction of chromosomal aberrations by REs. The different capacities of REs to induce chromosomal aberrations are probably correlated with the number of recognition sites in the genome. Most restriction endonucleases (REs) recognize tetra-, penta- or hexa-nucleotide sequences in dou- ble-stranded DNA molecules (Roberts, 1983). DNA in chromatin and in metaphase chro- mosomes in vivo is cut by REs, indicating that the restriction sequences can be recognized by REs, irrespective of the association of DNA with pro- teins (Lica and Hamkalo, 1983; Lipchitz and Axel, 1976). Treatment of methanol/acetic acid-fixed metaphase chromosomes of mammalian, including human origin with REs, leads to the production of banding patterns most probably by the loss of DNA fragments cut off from the chromosomal DNA (Bianchi et al,, 1984; Kaelbling et al., 1984; Lima de Faria et al., 1980; Miller et al., 1983). Recently, Bryant (1984) and Natarajan and Obe (1984) have shown that REs are able to induce chromosomal aberrations when introduced into cells by using inactivated Sendal virus prepara- tions as the permeabilizing agent. With this experi- mental schedule one cannot rule out that some of the aberrations may result from the interaction of viral components with the RE-cut DNA. Treat- ment of isolated nuclei with REs leads to cutting of DNA without addition of permeabilizing agents (Lipchitz and Axel, 1976). We have shown that Neurospora crassa endonuclease (EC 3.1.30.1) can reach the nuclei of human peripheral lymphocytes and Chinese hamster ovary (CHO) cells without using a permeabilizing agent (Nowak and Obe, 1984; Nowak et al., 1984). In this communication we show that treatment of CHO cells with REs without a permeabilizing agent leads to chromosomal aberrations, indicat- ing that the aberrations are induced by the REs and are not influenced by the presence of viral nucleic acid. We also show that various REs have widely different capacities for inducing chromosomal aberrations which probably reflects the number of respective recognition sites in the genome. Materials and Methods (1) Restriction endonucleases (REs) The REs used are listed in Table 1 together with their recognition sites, the suppliers and the buffers in which they are shipped according to the 0027-5107/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)