hnRNP A1: Lysates

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.1, 3, 4 Isolated hnRNPs consist of protein groups named A to U and many of these protein groups consist of more than one isoform. The major steady-state proteins of the isolated hnRNP complex are A1, A2, B1, B2, C1, and C2, with a range of molecular weight starting with 34 kDa up to 43 kDa.1, 3, 4 hnRNP-A1 is important in pre-mRNA processing and in mRNA export from the nucleus. The protein binds to its RNA target through a consensus RNA-binding site UAGGGU. The protein contains a 38-amino acid domain called M9, which is important for the interaction with the transportin protein, and therefore, for its import and export from the nucleus. RanGTP mediates dissociation of hnRNP-A1 from transportin. hnRNP-A1 is ubiquitously expressed with a higher expression in proliferating and/or transformed cells than in differentiated tissues.5