Adds poly(A) tail to the 3' end of many RNAs, which usually targets these RNAs for decay. Plays a significant role in the global control of gene expression, through influencing the rate of transcript degradation, and in the general RNA quality control. ATP + RNA(n) = diphosphate + RNA(n)-3'-adenine ribonucleotide Belongs to the tRNA nucleotidyltransferase/poly(A) polymerase family. Extended N-terminus. Extended N-terminus.