The sequence that controls the copy number of the linked DNA in the vector, is termed :

The sequence that controls the copy number of linked DNA in the vector is the ori site. It is also required for initiation of DNA replication. Therefore, for the multiplication of any alien piece of DNA in an organism it needs to be a part of a chromosome(s) which has a specific sequence known as ‘origin of replication’.

Selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli.

In order to link the alien DNA, the vector needs to have very few, preferably single, recognition sites for the commonly used restriction enzymes.

Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA. The palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same.