What are the 4 essential components of a bacterial cloning vector (plasmid)?

Use the same restriction enzyme for both the excision of the gene of interest and the plasmid you are using to be the vector. Restriction enzymes are enzymes that nick DNA sequences at specific sequences. They will only recognise one sequence of bases, but are pallindromic- i.e. will recognise the same sequence backwards as well.

As you use the same restriction endonuclease for both the plasmid and the gene of interest the ends will be complementary, as most restriction enzymes used for biotechnology will leave sticky ends- exposed bases at the end of the sequence that will ligate in the presence of ligation enzymes.

Cloning vectors have selectable marker genes on them.This can be a fluorescent protein, or a marker for antibiotic resistance. So if these organisms are grown on an agar plate that has the antibiotic that the bacteria have been transformed to resist then only those bacteria will grow. Other bacteria present that have not been transformed or are not resistant to the antibiotic will die.

You can then be sure that if protein synthesis has been carried out you can assay for your particular protien of interest.

hope this helps