ribonucleoprotein

ribonucleoprotein (RNP) Any complex of protein and RNA that forms during the synthesis of RNA in eukaryotes; the protein is involved in the packaging and condensation of the RNA. Certain RNPs are restricted to the nucleus whereas others are found in both the nucleus and the cytoplasm. The most common RNP occurring in the nucleus is heterogeneous nuclear RNP (hnRNP), which consists of protein bound to the primary transcript of DNA (see transcription). It may be associated with small nuclear RNP (snRNP), which is involved in the removal of intron sequences from the primary transcript to form messenger RNA, which eventually leaves the nucleus (see RNA processing). A third type, small cytoplasmic RNP (scRNP), is found in the cytoplasm; examples include signal recognition particles – complexes of a single RNA and several proteins that help newly synthesized polypeptides to enter the endoplasmic reticulum (see signal hypothesis). See also heterogeneous nuclear RNA.