Drybench Plasmid.
How to read a plasmid map
A plasmid map is a drawing of a circular DNA molecule with its parts marked on it: where it is copied from, what lets you select for it, where an insert goes and the sites that cut it.
The ring and its numbers
A circular plasmid is drawn as a ring numbered from base 1, with positions counted clockwise along one strand, the top strand. A circle has no ends, so base 1 is only a convention taken from the sequence record, and a feature can run across it.
Parts are drawn as arcs or arrows. An arrow pointing clockwise reads along the top strand; one pointing anticlockwise reads along the bottom strand. Short ticks with names are restriction enzyme sites; an enzyme that cuts the ring once is a unique cutter, the kind used to open a plasmid at one place.
The parts a cloning vector needs
An origin of replication lets the plasmid be copied in its host. A selection marker, such as the bla gene that makes bacteria resistant to ampicillin, lets only cells carrying the plasmid grow. A multiple cloning site is a short stretch packed with unique restriction sites where an insert is placed, often beside a promoter that can express it.
pUC19, 2,686 base pairs, has all of these in a compact form: a ColE1-type origin, bla, and a lac region holding the cloning site (Vieira and Messing 1982; Yanisch-Perron et al. 1985).
Reading the evidence
On this site each feature on a map is a match to a part taken from a public sequence record, shown with its identity and coverage. A part the library does not hold is not drawn, so a feature missing from the map is not proof that the plasmid lacks it.
See it on a real plasmid
Open pUC19 and walk its features with the arrow keys; the feature table lists the same parts as text.
The genes drawn on a map are copied into RNA before a protein is made; the tour shows RNA polymerase II doing it in a human cell.
References
- Vieira J, Messing J. The pUC plasmids, an M13mp7-derived system for insertion mutagenesis and sequencing with synthetic universal primers. Gene 1982;19:259-268. PubMed 6295879
- Yanisch-Perron C, Vieira J, Messing J. Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13mp18 and pUC19 vectors. Gene 1985;33:103-119. PubMed 2985470
Statements summarised by the site's builder from the references, for scientific review.