Heterochromatin heterogeneity inTriturus marmoratus(Urodela: Salamandridae) demonstrated with specific DNA-binding fluorochromes and «in situ» restriction endonuclease/nick translation

Abstract

SUMMARY -The chromosomes of Triturus marmoratus have been studied using base-specific fluorochromes, and restriction enzyme digestion followed by nick translation to reveal the sites of specific DNA sequences. Much of the heterochromatin of this newt contains sufficient concentrations of AT-and GC-rich DNAs to be detected by specific fluorochromes. Our application of the restriction enzyme/nick translation to newt chromosomes for the first time shows that this procedure is particularly valuable for studying the organisation of heterochromatin in these organisms. The centromeres of all chromosomes except those of pairs 10, 11 and 12 had similar properties; a positive reaction with DA/DAPI, chromomycin/DA, Hae III/nick translation and Hinf 1/nick translation, but a negative reaction with Eco Rl/nick translation. The reactions of the centromeres with the restriction enzyme/nick translation procedures can be correlated with the known properties of the satellite DNAs contained in these regions. On the other hand, the large heteromorphic blocks of heterochromatin on the long arms of chromosome I, were shown to be highly heterogenous when digested with Hae III or Eco RI and nick translated.