Structure and expression of the gene (HNRPA2B1) encoding the human hnRNP protein A2/B1

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2 is a major nuclear protein and one of the major components of the hnRNP core complex in mammalian cells. We first determined the complete sequence of the human gene for hnRNP protein A2 (HNRPA2B1). The human HNRPA2B1 gene exists in a single copy over 9 kb in length. The gene was split into 12 exons, including a 36-nucleotide mini-exon, which was specific to the hnRNP protein B1, providing genetic evidence that the B1 mRNA was generated from the primary HNRPA2B1 transcript by alternative splicing. The 5' region of HNRPA2B1 was GC-rich and contained several DNA motifs for the binding of several transcription factors, which included 2 CCAAT boxes and no TATA sequences. The 5' ends of the mRNA were mapped to multiple positions. These structural features are characteristic of promoter regions of housekeeping genes. Northern blot and RT-PCR analyses of the HNRPA2B1 transcripts revealed levels of B1 mRNA from 2 to 5% of total A2/B1 transcripts and showed that both A2 and B1 mRNAs were transcribed in all human cell lines and mouse tissues studied. The structural and evolutionary characteristics of the A2 and A1 proteins as they relate to each other are discussed.