Small nucleolar RNAs are stable RNAs of around 1-200nt which in the form of snoRNPs determine cleavage and modification sites in ribosomal RNA (rRNA) processing. There are two main classes of snoRNAs: box C/D and box H/ACA snoRNAs which are responsible for 2'-O-ribose methylation and pseudouridylation of rRNAs). The specificity of where the modification of rRNA occurs depends on base-pairing between the snoRNA and the target sequence of the pre-rRNA.

Figure showing box C/D and box H/ACA snoRNAs

Plant snoRNA gene organisation differs substantially from that in vertebrates and yeast in that the vast majority of genes are organised as polycistronic snoRNA gene clusters. Polycistronic genes are transcribed together as a precursor snoRNA (pre-snoRNA) transcript. Processing of polycistronic pre-snoRNAs occurs via endonucleolytic cleavage between the individual snoRNAs, followed by exonucleolytic trimming to produce the mature snoRNA.

In all eukaryotic organism studies to date, there are snoRNAs which do not contain sequences complementary to rRNA. These snoRNAs are called ‘orphan’ snoRNAs and evidence is accumulating in, for example, human, that these snoRNAs may regulate mRNA transcripts and even alternative splicing. We are investigating the function of plant orphan snoRNAs.