Murine Stat1 encodes four variant proteins: exon structure and expression of variant transcripts in BMMs. (a) Genomic arrangement of murine Stat1 on the plus strand of mouse chromosome 1. Probe track indicates the exon junctions spanned by oligoprobes on the splicing array. (b) Variant transcripts are indicated by boxed exon cartoon. Stat1a is a 749 amino acid protein initiating from exon 1A. Stat1b is 712 amino acids, terminates at exon 23, truncating carboxyl-terminal 37 amino acids. Isoform c is 755 amino acids with alternate initiation at exon 1B (open box), and the insertion of an additional 6 amino acids (VFVPFQ) in the DNA binding domain by using cryptic splice site upstream of exon 17 (grey exon box). Isoform d is a 177 amino acid protein that skips exon 7 and terminates at exon 9. There are at least four noncoding transcripts observed, initiating from exons 1, 19, and 22 (not shown). (c) Scatter plot shows the distribution of expression detected by each probe. The average signal of each probe (unstimulated bone-marrow derived macrophages (BMMs) and BMMs subjected to seven hours of stimulation with lipopolysaccharide (+7 hrs LPS); x axis) was plotted against the normalized ratio of +7 hrs LPS/unstimulated BMM (y axis). Triangles indicate junction probes and exon probes are indicated by black squares. Differential expression was determined using a t test cutoff of P < 0.05.