Vectors & Plasmids Sequences and Maps

Many public vecotrs have been collected from public reports and annotated with Vector NTI software.

The terms plasmid and vector are often used interchangeably, but their meanings are slightly different. A plasmid is an extra-chromosomal DNA molecule found in bacteria (Sambrook and Russell, 2001). Plasmids and chromosomes are replicated using the same enzymes, but plasmids are replicated and inherited independently from the bacterial chromosomes. Normally a bacterium will have only one copy of its chromosome but it can have multiple copies of a plasmid.

In nature, plasmids usually carry gene(s) that are beneficial to, but not absolutely required by, the cell in which they reside. For example, bacterial antibiotic resistance genes are often carried on plasmids. For more detailed background on plasmids and vectors please see.

A vector, in molecular biology, refers to a plasmid that is engineered to make it a more useful tool for molecular biologists (all vectors are plasmids, but not all plasmids are vectors). Vectors are designed for a variety of applications including easy cloning of foreign DNA and easy expression of foreign proteins.

For cloning purposes, we need to know what features a vector has and their relative positions in the vector. We represent this information visually using a plasmid or vector map, which is showing the relative positions of key cloning features. Maps are usually constructed using the plasmid's DNA sequence.

In maps, plasmid bases are numbered sequentially, in a clockwise fashion, starting with base 1 and ending on the base immediately counter-clockwise to base 1. That is, if a plasmid is 3000 base pair (bp) in size it will have bases numbered 1 – 3000. Map positions of various vector features are indicated relative to their distance from base 1.