Homing endonucleases are a group of site-specific endonucleases that initiate homing, a nonreciprocal transfer of its own gene into a new allele lacking this gene. This work describes a novel phage T4 endonuclease, SegD, which is homologous to the GIY-YIG family of homing endonucleases. Like other T4 homing endonucleases SegD recognizes an extended, 16 bp long, site, cleaves it asymmetrically to form 3′-protruding ends and digests both unmodified DNA and modified T-even phage DNA with similar efficiencies. Surprisingly, we revealed that SegD cleavage site was identical in the genomes of segD^– and segD⁺ phages. We found that segD gene was expressed during the T4 developmental cycle. Nevertheless, endonuclease SegD was not able to initiate homing of its own gene as well as genetic recombination between phages in its site inserted into the rII locus.

归巢核酸内切酶是一组启动归巢的位点特异性内切核酸酶，归巢是将自身基因不可逆地转移到缺少该基因的新等位基因中。这项工作描述了一种新型的噬菌体T4核酸内切酶SegD，它与归巢核酸内切酶的GIY-YIG家族同源。像其他T4归巢核酸内切酶一样，SegD识别一个16 bp长的延伸位点，不对称地对其进行切割以形成3'突出的末端，并以相似的效率消化未修饰的DNA和修饰的T-even噬菌体DNA。令人惊讶的是，我们发现segD ^–和segD ⁺噬菌体的基因组中SegD切割位点是相同的。我们发现，SEGD该基因在T4发育周期中表达。然而，核酸内切酶SegD不能启动其自身基因的归巢以及插入rII基因座的噬菌体之间的基因重组。