On the physical structure of λ recombinant DNA

Summary

Crosses of sus O29xcI26 sus O125 with ¹⁵N¹³C labelled phages have been performed in ¹⁴N¹²C medium with conditions designed to prevent the duplication of the infecting chromosomes (less than 4% duplication among the mature phages) to determine how much of the recombinant molecule is inherited from each parent, and how much is newly synthesized.

Both the rec and the red mediated recombinants have 5% newly synthesized DNA, while at least 10% of the DNA is inherited from one parent and at most 85% from the other. The O gene is at 18.5% (or more) from the right end of λ DNA (Table 2).

The genetic structure of the recombinants in these types of crosses was analyzed: I. sus O29 tsR2xcI26 sus O125 II. sus O29xcI26 sus O125 tsR2.

The double heterozygotes in cI26 and tsR2 regions were (almost) always $\frac{{cl26 + }}{{ + tsR2}}$ in cross I and $\frac{{cl26tsR2}}{{ + {\text{ }} + }}$ in cross II (Table 3). The rec and red system seem different in some aspects of the regulation of the recombination process.

These results suggest the following Partial Hybridization model for both rec and red mediated recombination:

• a) The first step in recombination is a hybridization of the single strand of one parent molecule to the other parent DNA. The hybridization starts from one end of the molecule.

• b) The mismatched base pairs formed in this hybrid can be repaired through a mechanism of excision and resynthesis.

The model can explain qualitatively the high negative interference phenomenon. A critical analysis of the published results in λ, T1, and T4 shows that this model can explain the experimental results much better than does the Break and Join model.