Practice question

Homing endonuclease recognizes an extended homing site, typically 14-40 base pairs, corresponding exactly to the intron insertion locus in intron-free allele. Recognition sequence spans cleavage site, ensuring endonuclease cuts only alleles lacking intron, because presence of intron disrupts site. Cleavage generates 4-base 3' overhangs or blunt ends, activating homologous recombination machinery. High specificity prevents widespread genome toxicity yet tolerates degeneracy for spread to related sites. Cellular repair copies intron plus flanking homology, propagating element efficiently. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.