mRNAs with 3′ UTR extensions tend to have weaker poly(A) signals. (A) Composition of proximal cleavage sites of 1409 transcripts with 3′ UTR extensions, distal cleavage sites of 1409 transcripts with 3′ UTR extensions, and cleavage sites of expressed transcripts without 3′ UTR extensions. (B) Frequency of occurrence and distribution of AAUAAA-like motifs across 50-nt upstream sequences of cleavage sites. The −20 locus is indicated by red line. (C–E) Nucleotide composition of 100 nt up- and downstream flanking sequences of: (C) proximal cleavage sites of 1,409 transcripts with 3′ UTR extensions; (D) distal cleavage sites of 1409 transcripts with 3′ UTR extensions; and (E) cleavage sites of expressed transcripts without 3′ UTR extensions. The −20 locus, −7 locus, and −1 locus are indicated by red lines. (N.S.) not significant.
