In situ nick translation of metaphase chromosomes with biotin-labeled d-UTP

Limited nick translation experiments on fixed chromosomes were performed. Sites of preferential DNase-I nicking were made visible by the incorporation of biotin-labeled dUTP and subsequent binding of the streptavidin-peroxidase complex. This procedure leads to a banding pattern on the chromosomes which is strongly DNase-I concentration dependent. Along the chromosome arms, regions of enhanced DNase-I sensitivity alternate with regions of lower DNase-I sensitivity. No complete G- or R-type banding pattern was observed. The easily identifiable human Y chromosome was studied more intensively. Compiled data show the heterochromatin of the Y chromosome stained as heavily as the euchromatin. The boundary between the eu- and heterochromatin on the long arm appears to be a site of preferential DNase-I sensitivity.