Fig. 1.

Clusters of U7 snRNA genes in Xenopus tropicalis (A) and Danio rerio (B) taken from the USCS Genome Browser (http://genome.ucsc.edu/). The “U7” track shows BLAST matches of the U7 snRNA sequences; “Repeat-Masker” refers to annotated repetitive sequence elements; the “RefSeq” track shows the intron/exon structure of protein-coding genes; the “Conservation” panel displays PhastCons score measuring sequence conservation across vertebrates. We refer to the data track description at the USCS Genome Browser for technical details.