YEAST RNASE H(35) IS THE COUNTERPART OF THE MAMMALIAN RNASE HI, AND IS EVOLUTIONARILY RELATED TO PROKARYOTIC RNASE HII

We cloned the Saccharomyces cerevisiae homologue of mammalian RNase HI , which itself is related to the prokaryotic RNase Hn, an enzyme of un known function and previously described as having minor activity in Es cherichia coli, Expression of the corresponding yeast 35 kDa protein ( named by us RNase H(35)) in E. coli and immunological analysis proves a close evolutionary relationship to mammalian RNase HI, Deletion of t he gene (called RNH35) from the yeast genome leads to an about 75% dec rease of RNase H activity in preparations from the mutated, still viab le cells, Sequence comparison discriminates this new yeast RNase H fro m earlier described yeast enzymes, RNase H(70) and RNase HI, (C) 1998 Federation of European Biochemical Societies.