Integration of the 1B4 provirus occurs in an intron of the hnRNP A2/B1 gene. (A) Schematic representation of upstream flanking sequence isolated by inverse PCR (1B4 Flanking) shows that the 1B4 provirus integrated 159 nucleotides into an intron of the hnRNP A2/B1 gene. Exon and intron sequences are indicated by the black box and thin line, respectively. Nucleotide numbers correspond to the cDNA sequence in Figure 1. (B) Genomic sequences are colinear with the cloned cDNA sequences for 64 nt. (shaded region) until a consensus 5' splice site at which point they diverge.