Figure 7

Association of splice sites in human mRNAs with strong and cryptic splice sites identified in full-length ERVs. Upper and lower panels are for sense and antisense ERVs, respectively. ERVs are shown in approximate order of origin or most recent activity. Dashed lines represent the fraction of simple AG and GT splice site motifs in the consensus ERV that are cryptic. Variability indicated is calculated by Poisson statistics. HERV-L is represented by four consensus elements (see Materials and methods). Old ERVs, such as MLT1 and HERV-L, exhibit splicing exclusively at cryptic splice sites. mRNA splicing within younger elements, such as THE1A, HERV-E, and HERV-H, is found at both strong and cryptic sites. The recently active ERVs, HERV9 and HERV-K (HML-2), show no splicing activity at either strong or cryptic splice sites when found in the antisense direction in introns, while these ERVs demonstrate significant splicing activity when found in the sense direction.