Constantinesco F, Forterre P, Koonin E V, Aravind L, Elie C
Institut de Génétique et Microbiologie, UMR CNRS no8621, Bâtiment 409, Université Paris-Sud, 91405 Orsay cedex, France.
Nucleic Acids Res. 2004 Feb 27;32(4):1439-47. doi: 10.1093/nar/gkh283. Print 2004.
We showed previously that rad50 and mre11 genes of thermophilic archaea are organized in an operon-like structure with a third gene (nurA) encoding a 5' to 3' exonuclease. Here, we show that the rad50, mre11 and nurA genes from the hyperthermophilic archaeon Sulfolobus acidocaldarius are co-transcribed with a fourth gene encoding a DNA helicase. This enzyme (HerA) is the prototype of a new class of DNA helicases able to utilize either 3' or 5' single-stranded DNA extensions for loading and subsequent DNA duplex unwinding. To our knowledge, DNA helicases capable of translocating along the DNA in both directions have not been identified previously. Sequence analysis of HerA shows that it is a member of the TrwB, FtsK and VirB4/VirD4 families of the PilT class NTPases. HerA homologs are found in all thermophilic archaeal species and, in all cases except one, the rad50, mre11, nurA and herA genes are grouped together. These results suggest that the archaeal Rad50-Mre11 complex might act in association with a 5' to 3' exonuclease (NurA) and a bipolar DNA helicase (HerA) indicating a probable involvement in the initiation step of homologous recombination.
我们之前表明，嗜热古菌的rad50和mre11基因以类操纵子结构组织，还有第三个基因（nurA）编码一种5'至3'核酸外切酶。在此，我们表明来自嗜热古菌嗜酸热硫化叶菌的rad50、mre11和nurA基因与编码一种DNA解旋酶的第四个基因共转录。这种酶（HerA）是一类新型DNA解旋酶的原型，能够利用3'或5'单链DNA延伸进行装载以及随后的DNA双链解旋。据我们所知，此前尚未鉴定出能够沿DNA双向移位的DNA解旋酶。HerA的序列分析表明它是PilT类NTPases的TrwB、FtsK和VirB4/VirD4家族的成员。在所有嗜热古菌物种中都发现了HerA同源物，并且除了一种情况外，在所有情况下rad50、mre11、nurA和herA基因都聚集在一起。这些结果表明，古菌Rad50-Mre11复合物可能与一种5'至3'核酸外切酶（NurA）和一种双极DNA解旋酶（HerA）协同作用，这表明其可能参与同源重组的起始步骤。
