Figure 2.

Highly expressed mRNAs have short poly(A) tails. (a) Tail-length distribution is different in pools of genes with distinct expression levels. The transcript abundance categories represent the highest expressed genes (n = 500), those closest to the median expression (n = 500), and lowest expressed (n = 500). All three distributions were significantly different (Mann-Whitney U test). (b) Global relationship between poly(A) length and abundance was measured by plotting the mean normalized abundance of bins of genes (n = 13,601 protein coding genes) divided by median tail lengths. (c and d) Heat maps demonstrating the interplay of the frequency of optimal codons (F_op) and tail size with transcript abundance (n = 13,421 protein coding genes) (c) and ribosome enrichment²⁵ (n = 13,370 protein coding genes) (d). (e) Violin distribution plots with inlaid box-plots (white dot represents the median) of all tail-length measurements in genes with different frequencies of optimal codons (F_op) and abundance levels. (f to h) C. elegans genes were classified according to codon optimization, demonstrating a significant relationship between translational efficiency and the cumulative distribution of poly(A) length (f), transcript abundance (g) and ribosome enrichment²⁵ (h). Normalized abundance was calculated as the log2 of the fold-change of the number of tags in a transcript over the median transcript level. P-values were calculated using the Mann-Whitney U test between each codon optimization category and all genes sampled. Poly(A) tail measurements, abundance, F_op, and ribosome enrichment for C. elegans transcripts are available in Supplementary Data Sets 1 and 2.