```r
   require(BSgenome.Hsapiens.UCSC.hg19)
   sequences <- getSeq(BSgenome.Hsapiens.UCSC.hg19, rowData(olaps))
   gcPerExon <- letterFrequency(unlist(sequences), "GC")
   gc <- relist(as.vector(gcPerExon), sequences)
   gc_percent <- sum(gc) / sum(width(olaps))
   plot(gc_percent, rowMeans(assay(olaps)), log="y")
   ```
   
   ```
   ## Warning: 252 y values <= 0 omitted from logarithmic plot
   ```
   
   ![plot of chunk summarizeOverlaps-gc](figure/summarizeOverlaps-gc.png)