Fewer positive target sites for genes with long 3' UTRs. The boxplot shows the lengths of 3' UTRs grouped by the number of potential target sites in the training dataset. Red boxes represent down regulated UTRs, whereas blue boxes represent unaffected UTRs. No down-regulated genes have more than 8 potential target sites and few down-regulated genes have long 3' UTRs (> 5000 nt). The range of potential target site number is from 1 to 28 plus 32 and 38.