Splicing regulation of the tat gene. Schematic of Tat pre-mRNA and the Tat1 spliced product (containing exons 1, 4 and 7) as an example, showing positions of introns (thick black line) and exons (large open boxes), splice donors (SD) and acceptors (SA), exonic splicing enhancers (ESE, dotted boxes), exonic and intronic splice silencers (ESS, hatched boxes; ISS, grey box) and the GAR splice enhancer (checkerboard box). Splicing factors which bind these splicing regulatory elements are given for each in parentheses. NB: ESE2 element is contained within ESS2 and this region contains overlapping binding sites for SC35 and hnRNP A1. Not to scale.