Asymmetric staining of Ctenomys chromosomes after treatment with AluI restriction nuclease

After treatment with the endonuclease AluI for 6 or 24 h, chromosomes of two populations of the South American rodent Ctenomys presented an asymmetric banding pattern after Giemsa staining. These asymmetric patterns were chromosome specific (each chromosome of a pair showed different banding pattern) but constant from cell to cell and between homologous chromosomes of the populations analysed. The nature of this peculiar staining is discussed in the light of the interaction between endonucleases and DNA in chromatin of fixed chromosomes.