Polysome disassembly in cell extracts of cricket male accessory gland during sucrose gradient centrifugation

The stability of polysomes in cell extracts of cricket (Acheta domesticus) male accessory gland has been examined by sedimentation through a variety of step and linear sucrose gradients. After prolonged centrifugation there is a considerable decline in polysome content with a concurrent increase in monosomes. The extent of the reduction is more severe in step gradients, although the polysomes that remain show a typical profile on linear gradients.Evidence is presented which indicates that the reduction in polysome content is not due to nuclease action. The presence of detergents can affect the extent of disassembly but is not the principal cause. Comparison of ³H]leucine pulse-labelled gluteraldehyde-fixed and unfixed polysomes subjected to extended centrifugation reveals a release of nascent label near the top of the gradients in unfixed preparations. At least part of this displaced material is present as peptidyl-tRNA, suggesting that forced dissociation of polysomes rather than premature termination of nascent chains occurs as a consequence of sedimentation pressures. Comparison of the distribution of polyadenylic acid (poly(A)) sequences in sucrose gradients following short- and long-term centrifugation shows a shift of poly(A) containing RNA out of the polysome and into the pre-monomer region. It is concluded that sucrose gradient sedimentation results in the disassembly of a portion of the polysome population in the tissue examined. The implications with regard to the study of nonpolysomal messenger ribonucleoprotein and monomeric ribosomes are discussed.