An assortment of RNA molecules assembled around newly transcribed RNA (pre-messenger RNA, or pre-mRNA) in the cell nucleus. The hnRNA associates with proteins to form heterogeneous nuclear ribonucleoprotein (hnRNP). After release from the chromosome and processing of the pre-mRNA by the spliceosome (see intron), the mature messenger RNA remains associated with various proteins, forming a messenger ribonucleoprotein (mRNP), which is then exported from the nucleus. The terms hnRNA and pre-RNA are sometimes used synonymously. See rna processing.