structure and function. They are 30–50 DNA helicases resolving different recombinogenic DNA structures. The RecQ helicases are key factors in a number of DNA repair and recombination pathways involved in the maintenance of genome integrity. In eukaryotes the number of RecQ genes and the structure of RecQ proteins vary strongly between organisms. Therefore, they have been named RecQ-like genes. Knockouts of several RecQ-like genes cause severe diseases in animals or harmful cellular phenotypes in yeast. Until now the largest number of RecQ-like genes per organism has been found in plants. Arabidopsis and rice possess seven different RecQ-like genes each. In the almost completely sequenced genome of the moss Physcomitrella patens at least five RecQ-like genes are present. One of the major present and future research aims is to define putative plant-specific functions and to assign their roles in DNA repair and recombination pathways in relation to RecQ genes from other eukaryotes. Regarding their intron positions, the structures of six RecQ-like genes of dicots and monocots are virtually identical indicating a conservation over a time scale of 150 million years. In contrast to other eukaryotes one gene (RecQsim) exists exclusively in plants. It possesses an interrupted helicase domain but nevertheless seems to have maintained the RecQ function. Owing to a recent gene duplication besides the AtRecQl4A gene an additional RecQ-like gene (AtRecQl4B) exists in the Brassicaceae only. Genetic studies indicate that a AtRecQl4A knockout results in sensitivity to mutagens as well as an hyperrecombination phenotype. Since AtRecQl4B was still present, both genes must have non-redundant roles. Analysis of plant RecQ-like genes will not only increase the knowledge on DNA repair and recombination, but also on the evolution and radiation of protein families
