Chromosome banding procedures commonly employ treatment steps in order to visualize the bands. In various cases, band-positive regions of chromosomes are observed after the latter are exposed to, e.g., acids, bases, salts, heat, or enzymes. Recently, mouse chromosomes treated with the antibiotic actinomysin D and the dye acridine orange demonstrated high resolution G-banding patterns by light microscopy. However, occasionally, banding can be produced with little or no treatment of the chromosomes. The present report describes the presence of bands in chromosomes of cultured cells whereby no treatment steps, as noted above, were employed. It is interesting that the history of the cells included their transformation by polyoma virus.Maintenance of virus-transformed Syrian hamster cell lines and their examination in the transmission electron microscope (TEM) was done in the Department of Biology of the Massachusetts Institute of Technology.
