The ribosomal protein uL11 is located at the basis of the ribosome P-stalk and plays a paramount role in translation efficiency. In addition, no mutant for uL11 is available suggesting that this gene is haplo-insufficient as many other Ribosomal Protein Genes (RPGs). We have previously shown that overexpression of Drosophila melanogaster uL11 induces the transcription of many RPGs and Ribosomal Biogenesis genes (RiBis) suggesting that uL11 might globally regulate the level of translation through its transcriptional activity. Moreover, uL11 trimethylated on lysine 3 (uL11K3me3) interacts with the chromodomain of the Enhancer of Polycomb and Trithorax Corto. uL11, Corto and RNA Polymerase II co-localize at many sites on polytene chromosomes. These data have led to the hypothesis that the N-terminal end of uL11, and more particularly the trimethylation of lysine 3, supports the extra-ribosomal activity of uL11 in transcription. To address this question, we mutated the lysine 3 codon using a CRISPR/Cas9 strategy and obtained several lysine 3 mutants. We describe here the first mutants of Drosophila melanogaster uL11. Unexpectedly, the uL11K3A allele, in which the lysine 3 codon is replaced by an alanine, displays a genuine Minute phenotype known to be characteristic of RPG deletions (longer development, low fertility, high lethality, thin and short bristles) whereas the uL11K3Y allele, in which the lysine 3 codon is replaced by a tyrosine, is unaffected. In agreement, the translation rate slightly decreases in uL11K3A but not in uL11K3Y. Deep-sequencing of RNA from wing imaginal discs shows enrichment in the GO categories glutathione metabolism for up-regulated genes in both mutants and regulation of transcription for down-regulated genes in uL11K3A. Furthermore, analysis of deregulated genes cis-regulatory sequences suggests that uL11 might regulate transcription of target genes in concert with the couple of transcription factors Mad/Med that mediate response to the Bone Morphogenetic Protein (BMP) signaling pathway.
Single amino-acid mutation in the Drosophila melanogaster ribosomal protein uL11: an insight in its transcriptional activity
