hnRNP C1 + C2: Proteins and Enzymes

RNA polymerase II transcripts in the nucleus are in complex with several proteins called heterogeneous nuclear ribonucleoproteins (hnRNPs). These proteins are important in biological activities such as transcription, pre-mRNA processing, cytoplasmic mRNA translation, and turnover. hnRNPs can be isolated either by immunoprecipitation or by sucrose gradient fractionation of cell extracts. When this is performed, the hnRNPs are isolated (consisting of protein groups named A to U), and many of these protein groups consist of more than one isoform. The major steadystate proteins of the isolated hnRNP complex are the A1, A2, B1, B2, C1, and C2 with a range of molecular weight starting with 34 kDa up to 43 kDa. The hnRNP-C proteins have a single RNP motif RNA-binding domain (RBD) of 80 to 100 amino acid long. The hnRNP -C proteins preferentially bind to uridine-rich RNA sequences. Oligomerization of the protein through leucine rich regions in its C-terminal end is important for RNA binding.4 Although its physiological action is unknown, mutation of the hnRNPC gene causes a embryonic lethal phenotype.