Model of IL12RB1 allele expression, processing and isoform function. (A) Human IL12RB1 is located on the p-arm of chromosome 19, and comprises exons 1-9, 9b, and 10-17. Shown is a karyotype image of chromosome 19, with the hatched arrows indicating the approximate position of IL12RB1. Depicted along the length of each IL12RB1 allele are the location and relative sizes of each exon and intron. (B) In primary human tissue, one IL12RB1 allele is silenced (represented by the gray exons of Allele 1) while and the other is transcriptionally active (represented by the colored exons of Allele 2). (C) The active allele is transcribed into a IL12RB1 pre-mRNA, which binds hnRNP H via G-tracts that are downstream of the Exon 9b poly(A) site. (D) The IL12RB1 pre-mRNA is the alternatively spliced into either Isoform 1 or Isoform 2, both of which promote IL12 responses.