MA plots of microarray data. (A-F) Plots were constructed from microarray data for heavy polysomal (HP) or total (T) RNA samples obtained for WT or degron mutant (4G) cells in projects I, II, or III. M is calculated for each gene as log2 (I1)-log2 (I2), where I1 and I2 are the signal intensities from arrays 1 and 2, and quantifies the ratio of intensities between the two microarrays. A is calculated as 0.5 (log2 (I1)-log2 (I2)), and quantifies the average intensity for each gene in the two arrays. Plotting M against A reveals the differences in intensities between the two arrays as a proportion of the average intensity for each gene. The variance (σ2) of M is shown in each plot.