Localization of AT-clusters in normal mouse chromosomes by netropsin prefixation treatment in vitro

Fetal fibroblasts of the NMRI mouse strain were treated in vitro with the oligopeptide antibiotic netropsin for different time periods before harvest. Netropsin led to centromeric elongation in all chromosomes of the murine karyotype except chromosome no. 1 and the Y chromosome. Only the centromeric C-bands are affected. Since netropsin is a specific probe for AT-clusters in duplex DNA and because netropsin linkage changes DNA conformation, the results show that AT-rich DNA is preferentially localized in the C-bands of the mouse karyotype. This confirms the data on hybridization of RNA complementary to light satellite DNA in this species. Differences in the extent of centromeric elongation by netropsin suggest that the quantity of AT-clusters varies between different chromosome pairs. Furthermore, netropsin pretreatment influences the orientation of chromosomes in metaphase plates.