Homogeneously staining regions and double minutes in a human cell line: chromatin organization and DNA content.

Homogeneously staining regions (HSR) and double minutes, two novel chromosome abnormalities, are believed to represent sites of gene amplification. The basic organization of chromatin in an HSR in a human neuroblastoma cell line was shown, by electron microscopy, to be similar to that in a normal chromosome. Double minutes from another human neuroblastoma cell line were found, by dry mass determination, to contain an average of 1.41 X 10(-14) g DNA. This quantity corresponds to 6.38 X 10(3) kilobase DNA per double minute.