Molecular characterisation of RecQ homologues in Arabidopsis thaliana

Members of the RecQ family of DNA helicases are involved in processes linke d to DNA replication, DNA recombination and gene silencing. RecQ homologues of various animals have been described recently. Here, for the first time for plants, we characterised cDNAs of all in all six different RecQ-like pr oteins that are expressed to different extents in Arabidopsis thaliana. Sur prisingly, three of these proteins are small in size [AtRecQl1, AtRecQl2, A tRecQl3-606, 705 and 713 amino acids (aa), respectively], whereas the two b igger proteins result from a duplication event during plant evolution [AtRe cQl4A and AtRecQl4B-1150 and 1182 aa, respectively]. Another homologue (AtR ecQsim, 858 aa) most probably arose by insertion of an unrelated sequence w ithin its helicase domain. The presence of these homologues demonstrates th e conservation of RecQ family functions in higher eukaryotes. We also detec ted a small gene (AtWRNexo) encoding 285 aa which, being devoid of any RecQ -like helicase domain, reveals a striking homology to the exonuclease domai n of human Werner protein, a prominent RecQ helicase of larger size. By mea ns of the two-hybrid assay we were able to detect an interaction between At WRNexo and AtRecQl2, indicating that activities that reside in a single pro tein chain in mammals might in plants be complemented in trans.