Mention the features that are required to facilitate cloning into a vector.

(N/A) $(i)$ Origin of replication $(ori)$: This is a specific $DNA$ sequence where replication starts. Any piece of $DNA$ linked to this sequence can be made to replicate within the host cells. It is also responsible for controlling the copy number of the linked $DNA$.
$(ii)$ Selectable marker: In addition to the origin of replication,a vector requires a selectable marker. This helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. Genes encoding resistance to antibiotics such as ampicillin,chloramphenicol,tetracycline,or kanamycin are considered useful selectable markers for $E. coli$.
$(iii)$ Cloning sites: To link the alien $DNA$,the vector needs to have very few,preferably single,recognition sites for the commonly used restriction enzymes. The presence of more than one recognition site within the vector will generate several fragments,which complicates gene cloning. The ligation of alien $DNA$ is typically carried out at a restriction site present in one of the two antibiotic resistance genes.