UTP20 and infection: On the contrary, 20 genes involved in ribosome biogenesis were significantly down-regulated (FDR<0.05, log2FC<0), with five of them showing less than half the expression level after infection: DDX21, HEATR21, RRS1, UTP20, WDR43. The proportion of significantly deregulated genes among the nucleolar biogenesis cluster was much higher than for all genes (Figure 4c; Figure 4d).