Distribution of AATAAA and single-base variants in 3′ ends of ESTs. (A) The hexanucleotide signals from the 3′ ends of four sets of cDNA sequences. The regions 10–50 bp from the polyadenylation sites were examined for the presence of AATAAA or its single-base variants. The 3′ ESTs from dbEST were divided into those starting with more than seven Ts (Tn > 7) and those without a T in the first position (T0). (B) The prevalence of each single-base variant in the cDNA termini with only one variant signal and no AATAAA within the 10–50-bp region from the poly(A) tail in each of four data sets is shown. The frequencies (%) of all 18 possible variants in each data set are shown beside bars. In vitro polyadenylation activities for each variant measured in the context of the SV40 polyadenylation signal are reproduced from the literature (Wickens et al. 1984; Sheets et al. 1990)
