A protein is expressed only under Mg²⁺ treatment, and not in untreated or mutant cells. This suggests:
Selective absence of protein in untreated samples and in magnesium transporter mutants, with induction only upon magnesium supplementation, indicates regulation beyond messenger RNA synthesis. If transcriptional control operated, mRNA levels would parallel protein induction. Splicing defects would generate size variants detectable on Northern blot, and increased mRNA decay would reduce total transcript abundance uniformly. Here transcript may be constitutively present but translationally silent due to 5' untranslated region riboswitch, upstream open reading frame, or magnesium-dependent transl
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
