ELECTRON-MICROSCOPY OF GIANT POLYRIBOSOMES FROM CHIRONOMUS-THUMMI SALIVARY-GLAND CELLS

The structural organization of giant translation units synthesizing high-molecular proteins isolated from Chironomus salivary glands was studied by the spreading technique and electron microscopy. Polyribosome complexes were made up from 79 to 146 ribosomes and had a pronounced gradient of increasing lengths of synthesizing protein molecules from the 5'- to the 3'-end mRNA. Many polyribosomes had a group of 2 to 7 nontranslating ribosomes at the 3'-end of the mRNA. The distribution of ribosomes along the mRNA and the packing of the protein molecule were not uniform. Giant polyribosomes may possibly be utilized in the research of the translational process.