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

<p>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, <i>Medicago truncatula</i>, <i>Arabidopsis thaliana</i>, and poplar. The three monocot plants are, in order, rice, maize, and sorghum. <b>A:</b> 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 (<i>r</i> = −0.53, <i>P</i><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>B:</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.