Senapathy proposed that the gene-expression regulatory sequences (promoter and poly-A addition site sequences) also could have originated from stop codons. A conserved sequence, AATAAA, exists in almost every gene a short distance downstream from the end of the protein-coding message and serves as a signal for the addition of poly(A) in the mRNA copy of the gene. This poly(A) sequence signal contains a stop codon, TAA. A sequence shortly downstream from this signal, thought to be part of the complete poly(A) signal, also contains the TAG and TGA stop codons.
Eukaryotic RNA-polymerase-II-dependent promoters can contain a TATA box (consensus sequence TATAAA), which contains the stop codon TAA. Bacterial promoter elements at ~10 bases exhibits a TATA box with a consensus of TATAAT (which contains the stop codon TAA), and at -35 bases exhibits a consensus of TTGACA (containing the stop codon TGA). Thus, the evolution of the whole RNA processing mechanism seems to have been influenced by the too-frequent occurrence of stop codons, thus making the stop codons the focal points for RNA processing.