Spread of Balbiani ring derived messenger RNA in Chironomus salivary gland cell cytoplasm.

We have investigated whether Balbian ring derived mRNA (75S RNA) of Chironomus salivary glands spreads to the different parts of the cytoplasm before or after attachment to the rough endoplasmic reticulum. Glands were fixed after in vivo administration of tritiated uridine and cytidine and the appearance of labelled RNA fractions in microdissected cytoplasm was measured. We chose central cytoplasm rich in rough endoplasmic reticulum (endoplasm) and peripheral cytoplasm with a low content of reticulum (basal zone). A peripheral spread of the mRNA on reticulum membranes would have moved the labelled RNA outwards with time. We found, however, a redistribution in the opposite direction, suggesting that the mRNA spreads over the whole cytoplasm before it attaches to the reticulum membranes. A similar redistribution occurs for the ribosomal subunits.