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. 2013 Nov 18;8(11):e79511. doi: 10.1371/journal.pone.0079511

Figure 3. The C/G and C/U ratios at the polyadenylation [poly(A)] tail attachment position of non-A-type poly(A) transcripts.

Figure 3

The 18 species, namely 12 animals, 3 dicot plants, and 3 monocot plants (3 cereals: rice, maize, and sorghum), were sorted from smallest (1) to largest (18) by the C/G ratios at the poly(A) tail attachment position of non-A-type poly(A) sites. The order of animal species from 1 to 12 is dog, rabbit, rat, zebrafish, mouse, cattle, zebra finch, orangutan, chicken, human, pig, and fruit fly. The three dicot plants are, in order, Medicago truncatula, Arabidopsis thaliana, and poplar. The three monocot plants are, in order, rice, maize, and sorghum. A: Comparison between the poly(A) tail attachment position C/G ratio and the messenger RNA (mRNA) C/G ratio. The mRNA C/G ratio is from the 99–nucleotide upstream region starting from, but not included, the poly(A) tail attachment position. There was an overall negative correlation between the poly(A) tail attachment nucleotide C/G ratio and the mRNA C/G ratio (r = −0.53, P<0.05). Note that in animals, the poly(A) tail attachment position C/G ratio (1.05 on average) on non-A-type poly(A) sites was only slightly (1.08 times) greater than the mRNA C/G ratio (0.97 on average). In plants, however, the poly(A) tail attachment nucleotide C/G ratio (5.73 on average) was about sevenfold higher than the mRNA C/G ratio (0.83 on average), suggesting that plants strongly selected C over G as the poly(A) tail attachment nucleotide. B: Comparison between the poly(A) tail attachment position C/U ratio of non-A-type poly(A) sites and the messenger RNA (mRNA) C/U ratio. The 18 species were sorted from smallest (#1) to largest (#18) by the C/G ratios at the poly(A) tail attachment position of non-A-type poly(A) sites, as in the top panel. Note that the C/U ratio of the poly(A) tail attachment position of non-A-type poly(A) sites was greater than the messenger RNA C/U ratio in most species and the results suggest a selection of C over U at the poly(A) tail attachment position.