Multiple Holliday junction resolving enzyme activities in the Crenarchaeota and Euryarchaeota

Holliday junction resolving enzymes are required by all life forms that cat alyse homologous recombination, including all cellular organisms and many b acterial and eukaryotic viruses. Here we report the identification of three distinct Holliday junction resolving enzyme activities present in two high ly divergent archaeal species. Both Sulfolobus and Pyrococcus share the Hjc activity, and in addition possess unique secondary activities (Hje and Hjr ). We propose by analogy with the two other domains of life that the latter enzymes are viral in origin, suggesting the widespread existence of archae al viruses that rely on homologous recombination as part of their life cycl e. (C) 2001 Federation of European Biochemical Societies. Published by Else vier Science B,V. All rights reserved.