Large-sized polysomes in Chironomus tentans salivary glands and their relation to Balbiani ring 75S RNA.

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Abstract
Polysomes from the salivary glands of C. tentans were investigated to determine whether Balbiani ring 75S RNA is incorporated into polysomal structures, and thus probably acts as mRNA. A new extraction technique for obtaining ribonucleoproteins was applied that gives a high yield of polysomes with only moderate degradation of the cytoplasmic, high MW RNA. The polysomes sedimented in a broad region (200-2000S) with a peak value of about 700S, which suggested that they were partly of very large sizes. This was confirmed by visualization of the polysomes in the EM 400S polysomes contained mainly 11-16 ribosomes, and 1500S polysomes about 60 ribosomes per polysome, but polysomes containing 100 or more ribosomes were also observed. Most of the cytoplasmic 75S RNA was located in polysomes, preferentially in the most rapidly sedimenting ones. From the available information on Balbiani ring RNA in cytoplasm and the present demonstration of 75S RNA molecules in polysomes, it was concluded that at least some Balbiani ring RNA, generated as 75S RNA within the Balbiani rings, eventually enters polysomes without being measurably changed in size. The present information on the potential amino acid coding sequences in 75S RNA is discussed in relation to the large size of the polysomes observed.