Studies on the efficiency of translation and on the stability of actin mRNA in mouse sarcoma ascites cells

CEREGHINI, S; GEOGHEGAN, T; BERGMANN, I.E.; BRAWERMAN, G.

BIOCHEMISTRY

Año: 1979 vol. 18 p. 3153 - 3159

0006-2960

The actin mRNA of mouse sarcoma ascites cells differs from the other abundant mRNA species with respect to its poly(A) content. It is enriched in chains with short poly(A) segments, and a substantial portion may not have any poly(A) at  all. In order to determine whether this unusual feature of the actim mRNA influences its physiological behavior, we studied actin synthesis in cells incubated under various conditions. Two treatments of the cells that reduce their capacity for polypeptide chain initiation, incubation in high salt and starvation, did not affect actin synthesis in any unique fashion. The synthesis of actin was relatively resistant to these treatments, as was the synthesis of some other abundant polypeptides. Different patterns of inhibition of polypeptide synthesis were obtained with the two treatments. The actin mRNA was also translated with relatively high efficiency in the reticulocyte cell-free system supplemented with polysomal RNA from ascites cells. Actin was by far the major polypeptide produced in this system, and its synthesis was not inhibited in the presence of excess mRNA. Prolonged incubation of the ascites cells in a culture medium caused a gradual decay in their capacity for actin synthesis. This was accompanied by corresponding losses in translatable actin mRNA. The poly(A)-containing and poly(A)-deficient components were affected to about the same extent. Other major mRNA species were not affected by this treatment. Addition of actinomycin D to the incubation medium prevented the loss of actin mRNA. It appears that this drug causes a stabilization of this RNA species. The changes in actin mRNA do not appear to be linked to the proliferative state, since rapidly growing and contact-inhibited mouse 3T3 cells showed the same relative rate of actin synthesis.