Question

In order to clone a DNA gene, it is inserted into a larger vector. Why should the vector used be larger?

Answer 1

A cloning vector is a genome that can accept the target DNA and increase the number of copies through its own autonomous replication. The vector must be capable of being stably maintained in an organism, and into which a foreign DNA fragment can be inserted for cloning purposes. The vector therefore contains features that allow for the convenient insertion or removal of a DNA fragment to or from vector such as restriction digestion sites, etc. Other than that, a vector must have an ORI site, a selectable marker site such as antibiotic resistance gene etc, a multiple cloning site (MCS) for DNA insertion, a reporter gene as well as expression elemements.

Size of a vector is a direct indication as how many features a vector has and what size of insert it can suitably take. For example, a pBR322, a plasmid vector is of size 4kb, it can only take inserts upto approx 15 kb in size, while YACs (yeast artificial chromosomes) can take up DNA of upto 3000 kb. Hence, the vector used should be suitable large so as to accomodate the DNA insert as well as its other features.