Ultrastructural analysis of membrane-bound polysomes in mouse "nonsecretory" myeloma (nonproducing type).

Using our electron microscopic method of polysome analysis we ascertained the numbers of membrane-bound polysomes and their constituent ribosomes in myeloma cells of J 606 (IgG3) and MOPC315 (IgA) parent cell lines and in their variants that did not produce and, accordingly, secrete either H- or L-chains. Both variants had far fewer membrane-bound polysomes than the respective parent lines. The polysome distribution curve drawn for each of these variants showed one peak at 5-6 ribosomes. In contrast to this finding, the distribution curves for the J 606 and MOPC315 parent lines gave two peaks. These observations on mouse myelomas strongly resembled those on human myelomas.