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Joined 2026-09-21 Message
Incoming links: Origin of replication
Origin of replication 2026-10-18
An origin of replication is a DNA region at which DNA replication is initiated. Its function depends on compatible cellular machinery.
Plasmid Created 2026-10-13 Updated 2026-10-18
A plasmid is an extrachromosomal DNA replicon: genetic material maintained by DNA replication separately from the host's main chromosomes. Separate copying does not mean independence of the host's enzymes or resources. Many plasmids are circular, but naturally occurring linear plasmids also exist.[ref]
Conservation of plasmid maintenance functions between linear and circular plasmids in Borrelia burgdorferi by Philip E. Stewart and others. Stewart, Chaconas and Rosa (2003), abstract opening sentence: natural linear and circular plasmids
Engineered plasmids can carry genes for genetic transformation and functional complementation. Typical laboratory plasmids combine an origin of replication, a selectable marker and a plasmid insert. These are engineering roles, not requirements that every natural plasmid carry an experimentally chosen selectable marker or plasmid insert.[ref]
Molecular Biology Reference by Addgene. Plasmid Elements, Figure 2 and table: origin, antibiotic-resistance gene, insert and promoter; description applies to engineered vectors
The useful separation is between keeping a DNA fragment, finding its carriers and testing its function. Molecular cloning uses propagation to recover more copies for study. Plasmid restriction mapping tests a proposed arrangement, while DNA sequencing examines its letters. A successful genetic transformation or a biological colony showing antibiotic resistance answers neither question completely. The yeast cross-species complementation experiment goes a step further by separating plasmid selection from a test of functional complementation.
Plasmid feature map 2026-10-18
A plasmid feature map records the positions of specified DNA features. Construct an original circular example of total length base pairs. Coordinates run clockwise from a chosen zero, and and label the same boundary. Positions here denote boundaries between base pairs, so the interval from 1000 to 2500 contains base pairs. This convention avoids counting both endpoints as additional material.
An original 6000-base pair plasmid feature map: copying, selection and a chosen plasmid insert occupy distinct regions
. Hypothetical engineered circular DNA, with clockwise boundary coordinates. Blue marks an origin of replication at 200–700; green marks a selectable marker at 3200–4000; orange marks the plasmid insert at 1000–2500. Abstract restriction enzymes A and B cut at the labelled boundaries: A at 1000; B at 2500 and 4500. Their recognition nucleotide sequences are unspecified. Neither the feature intervals nor the total length describe a real commercial construct. The ring records position, not the physical shape or three-dimensional conformation of DNA. Details.
The origin of replication is assigned to 200–700, the selectable marker to 3200–4000 and the plasmid insert to 1000–2500. Other positions are unspecified DNA, not empty gaps. Their lengths account for the entire circle:The first three terms are the marked regions; the last is all remaining material. Choosing a coordinate zero does not add a physical break. Rotating every coordinate by the same amount changes the drawing's labels without changing any distance around the plasmid.
A gene promoter must function in the recipient for the intended gene expression; copying a plasmid alone does not establish gene expression.[ref]
Molecular Biology Reference by Addgene. Plasmid Elements, Promoter Region row: recipient-dependent transcriptional machinery
The map therefore supports three separate questions: can the carrier persist, can carriers be recovered, and can the selected DNA perform the proposed task? The galactose induction comparison illustrates the third question in an actual yeast experiment. Replicon 2026-10-18