HETEROCHROMATIN HETEROGENEITY IN TRITURUS-MARMORATUS (URODELA, SALAMANDRIDAE) DEMONSTRATED WITH SPECIFIC DNA-BINDING FLUOROCHROMES AND IN-SITU RESTRICTION-ENDONUCLEASE NICK TRANSLATION

The chromosomes of Triturus marmoratus have been studied using base-sp ecific fluorochromes, and restriction enzyme digestion followed by nic k translation to reveal the sites of specific DNA sequences. Much of t he heterochromatin of this newt contains sufficient concentrations of AT- and GC-rich DNAs to be detected by specific fluorochromes. Our app lication of the restriction enzyme/nick translation to newt chromosome s for the first time shows that this procedure is particularly valuabl e for studying the organisation of heterochromatin in these organisms. The centromeres of all chromosomes except those of pairs 10, 11 and 1 2 had similar properties; a positive reaction with DA/DAPI, chromomyci n/DA, Hae III/nick translation and Hinf I/nick translation, but a nega tive reaction with Eco RI/nick translation. The reactions of the centr omeres with the restriction enzyme/nick translation procedures can be correlated with the known properties of the satellite DNAs contained i n these regions. On the other hand, the large heteromorphic blocks of heterochromatin on the long arms of chromosome I, were shown to be hig hly heterogenous when digested with Hae III or Eco RI and nick transla ted.