“…The most common example of this is the assembly of a genetic circuit from individual transcriptional units: for practical reasons, it is often advantageous to assemble each transcriptional unit separately (stage 1 of the assembly) and then combine the separate transcriptional units into a single construct (stage 2 of the assembly). Another example is when a transcriptional unit must first be assembled individually, and then combined with additional modules such as helper genes, , selection markers, ,,− replication origins for different hosts, , centromeres, , targeting sequences for genomic integration, ,,,,,, or origins of transfer ( oriT ).…”