Ribosomal RNA synthesis in human-mouse hybrid cells

Abstract

Human and mouse 28 s ribosomal RNA when extracted at room temperature have identical mobility in polyacrylamide gel electrophoresis, but when heated, the mobility of the human type changes, whereas that of the mouse does not. It was therefore possible to distinguish the 28 s RNA of the two species in mixtures and to examine the nature of the ribosomal RNA synthesized by human-mouse somatic cell hybrids. Only the mouse type of 28 s could be detected, even in hybrids with up to 35 human chromosomes per cell. Several possible explanations are considered; perhaps the most likely is that in these hybrids the transcription of human ribosomal genes is repressed.