Relationship between gene expression, essentiality and persistence. (A) Genes are classified into three groups based on their expression levels and CV. Here data from 5 cell cycle time points were pooled for the analysis of gene expression and CV from 3 replicates. The background hexbin density plot describes the relationship between CV and expression values for all genes. The red curve is a local regression of CV values as a function of expression (using the LOESS R package). Based on this fitting, genes are classified into three groups indicated by different colors. Most genes fall into the group in the middle, where their average CV remains constant at 0.23 (the blue dotted arrow). The group on the left has, on average, high CV, and shows negative correlation between CV and expression. This group is suggested to include background transcription noise. The group on the right consisting of highly expressed genes also shows significantly higher CV. (B) Gene expression versus essentiality. Box and whisker plot of expressions grouped by essential, high-fitness-cost and nonessential genes. (C) Hexbin plot showing genes expression versus persistence. The red trend curve is a local regression of median expression versus PI (LOESS R package). The horizontal bar distinguishes the highly expressed genes (>1,000x) from the others, whereas the vertical bars delineates less conserved (PI < 50) genes from persistent (PI >150) genes.