RNA polymerase II trans cripts in the nucleus are in complex with several proteins calledheterogeneous nuclear ribonucleoproteins (hnRNPs). These proteins are important inbiological activities such as transcription, premRNA processing, cytoplasmic mRNAtranslation, and turnover. hnRNPs can be isolated either by immunoprecipitation or bysucrose gradient fractionation of cell extracts.2, 4, 5 Isolated hnRNPs consist of proteingroups named A to U and many of these protein groups consist of more than oneisoform. The major steady-state proteinsof the isolated hnRNP complex are A1, A2, B1, B2, C1, and C2, with a range ofmolecular weight starting with 34 kDa up to 43 kDa.2, 4, 5 hnRNP-A1 is important inpre-mRNA processing and inmRNA export from the nucleus. The protein binds to its RNA target through aconsensus RNA-binding site UAGGGU. The protein contains a 38-amino acid domaincalled M9, which is important for the interaction with the transportin protein andtherefore, for its import and export from the nucleus. RanGTP mediatesdissociation of hnRNP -A1 from transportin. hnRNP-A1 is ubiquitously expressed with ahigher expression in proliferating and/or transformed cells than in differentiated tissues.6. Alternate Names: anti-Helix destabilizing protein antibody, anti-Heterogeneous nuclear ribonucleoproteinA1 antibody, anti-Heterogeneous nuclear ribonucleoprotein A1B protein antibody,anti-Heterogeneous nuclear ribonucleoprotein B2 protein antibody, anti-Heterogeneousnuclear ribonucleoprotein core protein A1 antibody, anti-hnRNP core protein A1antibody, anti-Nuclear ribonucleoprotein particle A1 protein antibody, anti-Single strandDNA binding protein UP1 antibody, anti-syncrip antibody.