Practice question

Lambda integrase integration pathway depends on elaborate nucleoprotein intasome rather than Int alone. Integration Host Factor heterodimer binds to attP arm regions inducing U-turn bending bringing distant Int binding sites P'1, P'2, H1 near core B and C sites. IHF bending reduces effective DNA persistence length, enabling cooperative interaction of Int monomers bridging attP and attB. Fis protein further modulates geometry. In absence of IHF, in vitro integration efficiency drops hundredfold. Therefore IHF serves as accessory factor essential for efficient prophage establishment, while excision additionally needs Xis for architectural remodeling.