The origins of introns and their evolutionary role remain unclear. In the November 6
They used the program to map intron positions onto homologous genes encoding proteins for which the three-dimensional structure is known. They applied the program to 665 nonredundant protein sequences in the Protein Data Bank and mapped over 8,000 introns. The result was a correlation of phase-zero introns with module boundaries in proteins, corresponding to ancient conserved regions (ACR). There was no correlation for phase-one or phase-two positions, or for non-ACR proteins (which presumably represent 'modern' genes).