Identification of additional regulatory RNPs that impact rRNA and U6 snRNA methylation

Ribosomes can be heterogeneous, and the major contributor to ribosome heterogeneity is variation in rRNA modification. There are two major types of rRNA modification, pseudouridylation and ribose methylation. In humans, the majority of these rRNA modifications are conducted by two classes of small nucleolar ribonucleoproteins (snoRNPs), which contain a guide RNA (small nucleolar RNA, snoRNA) complexed with proteins. Box H/ACA snoRNPs conduct pseudouridylation modifications and box C/D snoRNPs generate ribose methylation modifications. It is unclear how ribosome heterogeneity is accomplished in regards to the understanding of the signals and factors that regulate rRNA modifications. We have recently reported that a new class of RNP, that we term regulatory RNP (regRNP), may contribute to rRNA modification as well as the modification of nucleolar trafficked U6 snRNA, via interactions with snoRNPs. Here we report the identification of additional regRNP activities that influence the methylation of two sites within 18S rRNA, two sites within 28S rRNA and one site within U6 snRNA. These findings provide additional proof that regulation of snoRNP activity contributes to ribosome heterogeneity.