Differential location of nucleic acids within interchromatin granule clusters.

We have examined in great detail the distribution of nucleic acids within interchromatin granule clusters in different cell types by means of various immunocytochemical approaches. Using the in situ polyadenylate nucleotidyl transferase-immunogold technique for RNA detection or anti-RNA antibodies, we decisively demonstrate the presence of appreciable amount of RNA in clusters of interchromatin granules of untreated cells. Neither the in situ terminal deoxynucleotidyl transferase-immunogold technique nor anti-DNA antibodies, nor the in situ nick-translation technique for DNA detection have revealed any DNA in the interchromatin granule clusters. However, dispersed chromatin sensitive to DNase I are found at the borders and in the close vicinity of interchromatin granule clusters. The results indicate that interchromatin granule clusters should not be nuclear structures directly involved in RNA transcription but rather in some other steps of RNA metabolism.