Electron microscope localization of nuclear RNA's that shuttle between cytoplasm and nucleus and nuclear RNA's that do not.

Nuclear transplantations and electron microscope autoradiographv (EMRA) were utilized in order to localize and characterize small nuclear RNA's (snRNA) in ameba nuclei. A class of nonmigrating low molecular weight nuclear RNA's is associated with the structureless region of the nucleoplasm but not with the nucleoli, nuclear helices, or chromatin Thus, the role of these RNA's in genetic regulation is questionable A class of migrating RNA's (presumed, but not directly shown, to be low molecular weight) that shuttles between nucleus and cytoplasm is also not associated with nucleoli or helices but some radioactivity is associated with the chromatin It may be, therefore, that the shuttling RNA's are in some way involved in genetic transcription or replication.