Fig. 9.

Features associated with TSSs and PASs. The TSS is indicated by +1. The most common nucleotide at each position of the 15-nt core promoter motif is indicated. N means that there was no predominant nucleotide. The core motif associated with a TSS is followed by an AT-rich spacer, which distinguishes it from silent core motifs in the genome. The untranslated RNA leader sequence (UTR) preceding the ATG translation initiation codon varies greatly in length with a median size of 21 nt. The RNA U5NU motif (T5NT in DNA) can occur before or after the stop codon and signals transcription termination approximately 40 nt downstream. RNAs with and without the U5NU sequence frequently have a pyrimidine-rich sequence near the PAS.