The fate of patatin mRNA was investigated in slices of potato tuber since this mRNA appeared to be a potential example of a preexisting mRNA that is involved in the rapid formation of polysomes which occurs in such slices. Levels of patatin, which is the major storage protein in mature potato tubers, decreased slightly during the first 4 h after slicing but remained constant for the next 44 h. Analysis of products of in vitro translation showed that patatin mRNA was present and stable in the tuber cells even after several months of storage. The translational activity of patatin mRNA relative to total translational activity in total cellular RNA fraction increased transiently during the first hour and then decreased rapidly to undetectable levels within 6 h. By contrast, the activity in polysomal RNA fraction decreased immediately after slicing. The difference between the relative activities of patatin mRNA in total and polysomal RNA fractions during the first hour suggests that the extent of incorporation of patatin mRNA into polysomes was not in direct proportion to its abundance in the cells of the slices. Addition of actinomycin D to the slices did not prevent the transient increase in the translational activity of patatin mRNA in total RNA fraction at 1 h, indicating that the transient increase was not due to synthesis of patatin mRNA de novo after slicing. However, the inhibitor prevented the degradation of patatin mRNA in the slices. This result indicates that the synthesis of new mRNAs is necessary for the degradation of patatin mRNA.
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