Recursive splicing is a process in which large introns are removed in multiple 
steps by re-splicing at ratchet points--5' splice sites recreated after 
splicing. Recursive splicing was first identified in the Drosophila 
Ultrabithorax (Ubx) gene and only three additional Drosophila genes have since 
been experimentally shown to undergo recursive splicing. Here we identify 197 
zero nucleotide exon ratchet points in 130 introns of 115 Drosophila genes from 
total RNA sequencing data generated from developmental time points, dissected 
tissues and cultured cells. The sequential nature of recursive splicing was 
confirmed by identification of lariat introns generated by splicing to and from 
the ratchet points. We also show that recursive splicing is a constitutive 
process, that depletion of U2AF inhibits recursive splicing, and that the 
sequence and function of ratchet points are evolutionarily conserved in 
Drosophila. Finally, we identify four recursively spliced human genes, one of 
which is also recursively spliced in Drosophila. Together, these results 
indicate that recursive splicing is commonly used in Drosophila, occurs in 
humans, and provides insight into the mechanisms by which some large introns are 
removed.