To determine whether the presence of the indel affected transcription in vitro, transient transfection assays were carried out. First, the promoter region extending approximately −1.6 kb upstream of the translation start site was compared with that extending to −2.3 kb on the reference sequence, in DNA without the indel (Fig. 2). The additional 665 bp had a small but significant negative effect upon gene expression, reducing it to 87% that of the shorter fragment (P < 0.01). Next, the construct with the indel (3.1) was compared with its counterpart without the indel (2.3). The presence of the indel lowered transcription activity to 53% of that in its absence (P < 10−11).
