The ura4 gene and its nearby cluster of replication origins. The diagram is based on the nucleotide sequence of S. pombe cosmid c330 (EMBL accession number SPCC330). The numerical scale indicates nucleotide sequence position within SPCC330. Cut sites for selected restriction enzyme are shown in blue. The locations of the two characterized (ura4 and pmp20) and uncharacterized (SPCC330.07c and SPCC330.08) open reading frames and their putative directions of transcription are shown by the magenta arrows. Replication origins are indicated by green boxes. Lighter green boxes are more efficient chromosomal replication origins than darker green boxes [7,8,9]. The replication enhancer (RE) is shown in yellow.