The entire SV40 sequence was used as the reference genome to investigate the insertion of the SV40 small tAg present in GMO sample 1 and SV40 intron present in GMO sample 2. As shown in Fig. 4C, GMO sample 1 showed two separate locations of peaks, one spanning a region centered around ~2.7 kb and another centered around ~4.4 kb, where each location had a peak for each antibody tested. The region at ~4.4 kb is adjacent to the small tAg, the inserted element. The area around ~2.7 kb is in a region that exhibits sequence similarity to the mouse genome and most likely represents either an artifact of the alignment or an additional SV40 sequence present in the transgene but not originally annotated. In contrast to the peaks identified in GMO sample 1, the other two GMOs and all four wild-type samples had no peaks aligning to the SV40 genome. It is not unexpected that GMO sample 2 failed to have peaks aligning to SV40 even though it contained an intron of the SV40 genome since the histone antibodies used in these experiments are not known to bind to intronic regions.
The sequence for the entire human TPM3 gene was also used as a reference template for unmapped read mapping. GMO sample 1 contained a large peak located at the 5′ end of the TPM3 gene which is absent for all other samples ( Fig. 4B). Similar to the results for the human ACTA1 gene, minor background peaks (