Protein synthesis inhibitors and export of ribosomal subunits.

Puromycin and cycloheximide inhibit nuclear export of ribosomal RNA in Chironomus salivary gland cells like in mammalian cells. The drugs do not prevent other types of RNA like heterodisperse messengerlike RNA, 75-S RNA of Balbiani ring origin and 4-S RNA from appearing in the cytoplasm. Newly exported ribosomal subunits have previously been found to enter polysomes close to the nuclear envelope in these cells. The basis for the specific export-blocking action of the drugs may be that immediate engagement in polysomes is a prerequisite for export of ribosomal subunits.