Transcription specific differences visualized by fluorescence in situ hybridization pattern on interphase nuclei of different cell types. 
Application of a "formamide free" and thus "material preserving" in situ hybridization technique using the cDNA of the myf3 gene revealed the following results: Human rhabdomyosarcoma cells, characterized by a high expression of myf3 show intensive hybridization signals in their interphase. RNase treatment prior to hybridization considerably reduces the size of this signals. In comparison, isolated nuclei of human lymphocytes in which no need for the expression of this gene exists, show barely hybridization signals. Correspondingly, RNase treatment had no effect on hybridization pattern at all. In conclusion an increased transcription efficiency of a cell type specific gene is accompanied by a higher hybridization accessibility in the corresponding cell nuclei.