Metabolism of poly(A) sequences during 3T3 cell growth regulation

Abstract

The metabolism and the intracellular distribution of RNA-associated poly(A) sequences from contact-inhibited and serum-induced proliferating 3T3 cells were examined by hybridization with [ 3H]poly(U). Evidence is presented for the growth-specific changes in the ‘steady-state’ populations of poly(A) sequences as determined by this technique. The results indicate that reinitation of growth in 3T3 cells is accompanied by characteristic changes in total poly(A) content and the size of the ‘steady-state’ poly(A) sequence. The serum-induced state is characterized by: (1) a higher content of RNA-associated poly(A) sequences; (2) the redistribution of poly(A)-containing RNA species from sub-ribosomal to polysomal fraction; and (3) an overall shortening of the RNA-associated poly(A) sequences. The size distribution of newly synthesized poly(A) in both resting and serum-induced cells are similar even though there is a marked reduction in the size of steady-state poly(A) sequences of the RNA from growing cells. The suggestion that there is an enhanced poly(A) processing in serum-induced cells is further substantiated by an increase in poly(A) hydrolyzing activity in growing cells. These findings of the growth-specific cellular pattern of poly(A) sequences in RNA suggest a possible physiological role for the modulation of poly(A) size in the regulation of mRNA expression with respect to cell growth.