Today I learned something very very interesting about plasmids from Cathal Garvey:

The first recombinant plasmids were derived from natural occuring plasmids. That’s clear.

And they cut everything out that was not considered to be needed essentially. To get a standard-minimal vector of which all functions are known.

They also cut out the “Single  stranded origin” or SSO. This sequence makes the plasmid very stable.

The standard- often-used vector plasmids of today all are derived from those minimal plasmids (time after time more functions were added like LacZ’ MCS etc. ) .  But they lack the SSO.  Therefore they are very untsable. His words were “Plasmids wouldn’t even exist in the wild if they were that unstable. ”

“The available literature suggests that
unless a gene is particularly bad for a bacterium (toxic gene products,
overly strong promoters, etc..), the plasmid shouldn’t get lost just due
to growth and replication. You get less than 2% of cells without
plasmids after ~10-20 cycles of replication without antibiotic
selection, versus 80-99% for conventional plasmids.”



That’s amazing. I’ve never come across about this, but this totally makes sence.



Just to note this for those who didn’t know: Cathal had his own plasmid synthesized. It contains a SSO, of course.