Figure 1. A simplified representation of RNPs and their cellular functions. Small RNA protein complexes play important roles in mRNA maturation and the regulation of gene expression. In S. pombe, the RITS complex regulates centromeric heterochromatin formation. Small RNAs, such as the 7SK RNA, bind and regulate the transcription elongation factor (p‐TEFb) and, thus, transcription elongation. U snRNPs are the major components of the spliceosome, with U‐rich small nuclear RNAs (snRNAs) as RNA components. In the cytoplasm, mRNAs associate with ribosomal subunits to initiate the translation process. During translation, the signal recognition particle (SRP) RNP, with 7SL RNA as core RNA component, directs signal peptide‐containing nascent proteins together with associated ribosomes to the ER for further processing and cellular protein sorting. The miRNPs or RISCs are important regulators of gene expression, and guide post‐transcriptional gene silencing processes. The RNPs play further important roles for the processing or maturation of RNAs such as pre‐tRNAs, which are processed by RNase P. Small nucleolar RNPs (snoRNAs) or small Cajal body RNPs (scaRNAs) are essential for the maturation of ribosomal RNAs or snRNAs. The well‐known telomerase enzyme belongs to the snoRNPs; this restores the length of the telomeric ends of the chromosomes, which are reduced during each cell division cycle. For further details, see the main body of the text.