Which one of the following features is not required in a prokaryotic expression vector?

If bacterial cells are transformed with a mixture of linear and circular molecules resulting from a ligation reaction designed to produce a recombinant molecule

A recombinant protein is to be expressed under the control of the lac promoter and operator in a strain of E. coli having the genotype lacI⁺ crp⁺. Even in the absence of inducer IPTG, low levels of expression of the recombinant protein are seen (leaky expression). Which one of the following should be done to minimize such leaky expression?

Determine the correctness or otherwise of the following Assertion [A] and the Reason [R].
Assertion [A]: Dam methylase protects E. coli DNA from phage endonucleases.
Reason [R]: E. coli Dam methylase methylates the adenosine residue in the sequence "GATC".

The schematic of a plasmid with a gap in one of the strands is shown below:
Which of the following enzyme(s) is/are required to fill the gap and generate a covalently closed circular plasmid?
P. DNA ligase
Q. Alkaline phosphatase
R. DNA polymerase
S. Polynucleotide kinase