RNA modifications play a major role in gene expression. The existence of poly (A) additions at the 3′-end of messenger RNAs is well known and, more recently, poly (U) additions have been studied in some detail. However, by studying mitochondrial gene expression in Chlamydomonas reinhardtii, the team of Laurence Drouard, in collaboration with Olivier Vallon’s team at the “Institut de biologie physico-chimique“, discovered the addition of poly (C) at the end of mitochondrial messenger RNAs. This new type of post-transcriptional modification of messenger RNAs illustrates a biodiversity that is also reflected at the molecular level. This study was published on October 9, 2017, in the journal Nucleic Acids Research.