Restriction endonucleases: Powerful tools to induce chromosome markers

Abstract

The introduction of chromosome banding techniques about twenty years ago provided a simple and reliable method for chromosome identification, as well as highlighting structural and functional differences between chromosomal segments. On this basis, it has been possible to identify different chromosome markers and to analyse the extent of variation among different taxa at the chromosome level. Since 1968 when the first banding technique was employed, other more sophisticated methods have now become available which permit a deeper understanding of banding mechanisms down to the molecular level. Recently, techniques involving restriction endonucleases have been developed (REs) which may recognise specific nucleotide sequences along the chromosomes. Because of the high specificity of these enzymes, their in situ application on fixed chromosomes followed by Giemsa or Ethidium Bromide staining opens the possibility of obtaining a very large number of different banding patterns. To date, the main limitation of this technique lies in certain structural aspects involving the accessibility of REs to DNA, or chromatin extraction. More recently, yet another method with increased sensitivity and specificity has become available. In this method, sites of RE attack on chromosomes are identified by ‘nick translation’ (RE/NT) inducing banding patterns that do not depend on DNA extraction. Both applications assayed on several organisms have provided new chromosome markers as well as valuable information on structural and functional aspects.