Figure 6

The correlation between the breadth of expression in human tissues, the mean and the maximum expression, and the number of transcription factor binding sites. This figure consists of sixteen parts identified as ( a ) - ( p ). Four measures related to the breadth of expression were considered: ( a-b-c-d ) the breadth of expression at the cutoff of ten TPM, ( e-f-g-h ) the breadth of expression at the cutoff of 100 TPM, ( i-j-k-l ) the mean expression, and ( m-n-o-p ) the maximum expression. The number of transcription factor binding sites was estimated in four different approaches: ( a-e-i-m ) the total number, ( b-f-j-n ) the number of unique binding sites, ( c-g-k-o ) the total number excluding RNA polymerase II binding sites, and ( d-h-l-p ) the number of unique binding sites excluding the polymerase. The red line signified the linear model for the smoother line, while the blue line signified the non-linear model. The correlation between the number of transcription factor binding sites and the breadth of expression at the cutoff of ten TPM was robust under four different approaches to estimating the number of transcription factor binding sites. Interestingly, this correlation was driven by transcripts with between zero to twenty binding sites (r _p  = 0.42), and was much weaker for promoters with more than twenty sites (r _p  = 0.098). At the value of approximately twenty on the X-axis ( a-b-c-d ), the blue smoother (the non-linear model) reached a plateau and diverged from the red smoother (the linear model). This figure suggests that the correlation presented here was strongest at the cutoff for the breadth of expression of ten TPM, and was not biased by the polymerase or another individual transcription factor. The correlations with the mean expression were likely secondary to the correlation with the breadth of expression (see Results: Broadly expressed genes have more transcription factor binding sites).