上海科技大学知识管理系统

["RNase H1 has been acknowledged as an endoribonuclease specializing in the internal degradation of the RNA moiety within RNA-DNA hybrids, and its ribonuclease activity is indispensable in multifaceted aspects of nucleic acid metabolism. However, the molecular mechanism underlying RNase H1-mediated hybrid cleavage remains inadequately elucidated. Herein, using single-molecule approaches, we probe the dynamics of the hybrid cleavage by Saccharomyces cerevisiae RNase H1. Remarkably, a single RNase H1 enzyme displays 3 '-to-5 ' exoribonuclease activity. The directional RNA degradation proceeds processively and yet discretely, wherein unwinding approximately 6-bp hybrids as a prerequisite for two consecutive 3-nt RNA excisions limits the overall rate within each catalytic cycle. Moreover, Replication Protein A (RPA) reinforces RNase H1's 3 '-to-5 ' nucleolytic rate and processivity and stimulates its 5 '-to-3 ' exoribonuclease activity. This stimulation is primarily realized through the pre-separation of the hybrids and consequently transfers RNase H1 to a bidirectional exoribonuclease, further potentiating its cleavage efficiency. These findings unveil unprecedented characteristics of an RNase and provide a dynamic view of RPA-enhanced processive hybrid cleavage by RNase H1.","RNase H1 functions as an endonuclease degrading the RNA moiety within RNA-DNA hybrids. Here the authors find that RNase H1 displays 3 '-to-5 ' exonuclease activity. Moreover, RPA reinforces RNase H1's 3 '-to-5 ' nucleolytic rate and processivity and stimulates its 5 '-to-3 ' exonuclease activity."]