Fig. 3

Gene expression buffering mainly occurs post-translationally and buffered genes are enriched for post-translational modifications. a, b Scatter plots of inter-species divergence comparing between different molecular traits (RNA: transcript level, RPF: level of translation, protein: protein level). Each data point represents a gene and the position along each axis indicates the log₂ ratio between human and chimpanzee for each molecular trait. The color of each data point indicates whether the inter-species divergence for each gene is significantly buffered at the downstream molecular trait at a significance cut-off of FWER 0.05 (blue: significant, gray: not significant). c Post-translational buffering of human–chimpanzee divergence occurs much more frequently than translational buffering. Quantile-quantile plot of –log₁₀(p values) derived from testing for buffering of human–chimpanzee divergence (orange: translational buffering, blue: post-translational buffering). Observed p values (y-axis) were plotted against the null expectation (i.e. uniform distribution of p values) (x-axis). The red line marks the expected results from a scenario where no buffering was observed. d, e, f Post-translationally buffered genes are enriched for post-translational modifications and a higher within-species transcript level variation. Individual genes were grouped into bins according to their significance level of human–chimpanzee post-translational buffering (x-axis). Position of each data point along the y-axis indicated mean ± standard error. d Post-translationally buffered genes are not significantly enriched for amino acid substitutions. Ka (proportion of nonsynonymous substitutions out of all possible non-synonymous sites) calculated between human and chimpanzee was plotted against significance level of human–chimpanzee post-translational buffering. e Post-translationally buffered genes have more ubiquitination sites. Number of reported ubiquitination sites in human was plotted against significance level of human–chimpanzee post-translational buffering. f Potential impact of post-translational buffering on relaxation of transcriptional regulation. Post-translational buffering of inter-species divergence is more likely to occur to genes that have a higher within-species (human) variation at the transcript level. Standard deviation across YRI individuals (reflects level of variation in the population) of transcript level (orange) or that of protein level (black) was plotted against significance level of human–chimpanzee post-translational buffering