This is a myth. With our gene synthesis protocol we can not only synthesise genes of any length, we can also synthesise complete plasmids.
Synthetic genes are often created by assembling overlapping DNA oligonucleotides. With this method it is possible to create long fragments that will be finally assembled to one large synthetic gene. By adding a circularisation procedure it is therefore possible to even create complete plasmids of any length. As we routinely work with E. coli, your “gene” (i.e. the new plasmid) must harbour an E.coli selection marker and an origin of replication, of course.
Still the question remains, why someone would like to create his / her own plasmid. There are quite a few answers to that, like:
- Free choice in antibiotic resistance, promoters, origin of replication, etc.
- Free choice of the multiple cloning site, tailor-made for your projects
- No potential licensing issues if you want to use your plasmid commercially
- Sequence optimization of the vector to the host organism, to regulate the expression levels of the gene(s) (e.g. antibiotic resistance etc.)