Aprincipal problem with inserting an unmodified mammalian gene into a plasmid and then getting that gene expressed in bacteria is that

introns will remain inside the bacteria

Explanation:

Introns  are the remains of an RNA transcript that do not involve in coding and hence they are trimmed off once the protein is translated from the RNA molecule.

Introns are found more commonly in eukaryotic genomes as compared to bacterial and archaeal genes

Group I introns have an ability to invade tRNA, rRNA and protein  through its intervening sequences however their insertion into genes is phenotypically neutral.

cancer   is   essentially   uncontrolled   mitosis   of specialized cells

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