Plasmid feature map Created 2026-10-18 Updated 2026-10-20
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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.
Figure 1.
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:
(1)
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] 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.
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Yeast cross-species complementation experiment 2026-10-13
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Can a gene from Schizosaccharomyces pombe replace a missing function in Saccharomyces cerevisiae? A modern laboratory project tested functional complementation of methionine synthesis. For each tested gene deletion, the investigators compared plasmids carrying the corresponding Saccharomyces cerevisiae gene, a candidate Schizosaccharomyces pombe gene, and an unrelated gene. The first was a positive scientific control; the last was a negative scientific control. The paper describes this design rather than publishing a complete set of individual growth measurements. [ref]
The recipient biological strains also lacked the ability to make uracil. The pYES2.1/V5-His plasmids carried URA3, a gene restoring that ability, and used the GAL1 gene promoter to control the inserted gene. Initial plates lacked uracil but supplied methionine: this selected biological colonies containing plasmids without requiring successful methionine synthesis. Subsequent plates lacking methionine tested the missing function, comparing galactose induction with glucose conditions. Thus selecting for a plasmid and testing its functional contribution were separate operations. [ref]
The apparatus can be simple and informative. In the associated protocol, replica plating uses a block covered with velveteen to transfer small samples of biological colonies from a master plate onto plates with different nutrient conditions. Orientation marks preserve correspondence between locations; gentle contact limits the transferred material. The specified replicas omit uracil and methionine with either inducing sugar or glucose, and include a fresh glucose plate supplying methionine. The readout is growth at corresponding locations, not a direct measurement of enzyme activity. [ref]
Figure 1.
Separating plasmid selection from a yeast functional complementation test
. Original schematic of the reported experimental design, not copied growth data. All three constructs enter the same Saccharomyces cerevisiae gene deletion background. Plate labels identify distinct comparisons; arrows show sample transfer, not observed rescue. The candidate Schizosaccharomyces pombe outcome must be measured. Details.
The scientific controls answer different objections. Growth on the methionine-supplied replica checks survival and transfer. Rescue by the native gene checks that this biological strain and assay can reveal functional complementation. The unrelated gene tests whether carrying a plasmid alone is sufficient. Comparing induction conditions checks dependence on gene expression, although changing the sugar also changes metabolism: it is not an isolated change of gene expression in every other respect.
If the candidate gene restores growth while those comparisons behave as intended, it supplies a function sufficient for the tested growth requirement in this recipient. Failure to rescue is less decisive: the candidate protein might not be produced, might be altered by its attached tag, or might not work in this cellular context. The investigators therefore also used Western blots to examine protein production. A detected protein still does not establish correct protein folding or catalytic activity. [ref]
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