Differential activation of mRNA during maturation of bovine oocytes is correlated with changes in poly(A)-tail length

Abstract

Some aspects of the state of aggregation and functioning of polysomes have been investigated in preparations obtained from rat liver lobes subjected to ischemia. The incroporation of amino acid into protein is reduced in postmitochondrial supernatant fractions, microsomes, and C-ribosomes from ischemic livers. In the presence of cell sap from ischemic livers, normal C-ribosomes, but not normal microsomes, show a reduced incorporating capacity, which is not affected by a fivefold increase of the amount of cell sap in the incubation mixture. The analysis of the polysomal patterns shows that ischemia causes a progressive disaggregation of polyribosomes, with a reduction in the number of heavy aggregates and an increase of dimers and monomers. This disaggregation is best seen in the ribosomes recovered from the fraction bound to the membranes of the endoplasmic reticulum. The determination of RNA -used as a reference basis of the various subcellular fractions—shows that ribosomes are also reduced in number in preparations from ischemic livers. Bound ribosomes are more affected than the free forms. On the whole, ribosomes obtained from ischemic livers seem to be reduced in number, less aggregated, and less efficient in carrying out protein synthesis.