Figure 1.

The Red model for lytic cycle λ crosses conducted with blocked DNA replication in rec⁺ cells (1). (i) λ’s chromosome is cleaved at cos by the λ-encoded enzyme terminase; (ii) the cleaved chromosome is now a substrate for λ’s redα/β gene products, resulting in single-strand overhangs of 3′ polarity; (iii) the single-strand overhang now invades a homologous uncut chromosome; (iv) DNA polymerase I extends the invasive strand; (v) a nick is introduced, possibly through endonucleolytic activity residing in DNA polymerase I; DNA ligase then ligates the invading strand with the nicked strand; and (vi) the Redβ protein completes assimilation of the invading strand until assimilation is stopped by encounter with an incidental nick.