Observations on the structure of mechanically stretched chromatin fibrils

During the spreading of human chromosomes prepared from cultured human lymphocytes, the peripheral fibers attaching the chromosome to the support film are mechanically stretched. The stretching reveals structural elements of the fibers; some of these features have been described earlier, for extracted chromatin. The molecule of DNA is bared through stretching and binds labeled actinomycin D in consequence. One of the prominent features of stretched fibers is the irregularity of resulting structures. This paper further demonstrates the excellent resolution obtainable by electron impact evaporation of tungsten.