title: A novel mechanism underlies caspase-dependent conversion of the dicer ribonuclease into a deoxyribonuclease during apoptosis.
abstract: During C. elegans apoptosis, the dicer ribonuclease (DCR-1) is cleaved by the cell death protease CED-3 to generate a truncated DCR-1 (tDCR-1) with one and a half ribonuclease III (RNase III) domains, converting it into a deoxyribonuclease (DNase) that initiates apoptotic chromosome fragmentation. We performed biochemical and functional analyses to understand this unexpected RNase to DNase conversion. In full-length DCR-1, tDCR-1 DNase activity is suppressed by its N-terminal DCR-1 sequence. However, not all the sequence elements in the N-terminal DCR-1 are required for this suppression. Our deletion analysis reveals that a 20-residue α-helix sequence in DCR-1 appears to define a critical break point for the sequence required for suppressing tDCR-1 DNase activity through a structure-dependent mechanism. Removal of the N-terminal DCR-1 sequence from tDCR-1 activates a DNA-binding activity that also requires the one half RNase IIIa domain, and enables tDCR-1 to process DNA. Consistently, structural modeling of DCR-1 and tDCR-1 suggests that cleavage of DCR-1 by CED-3 may cause a conformational change that allows tDCR-1 to bind and process DNA, and may remove steric hindrance that blocks DNA access to tDCR-1. Moreover, a new DNase can be engineered using different RNase III domains, including the one from bacterial RNase III. Our results indicate that very distantly related RNase III enzymes have the potential to cleave DNA when processed proteolytically or paired with an appropriate partner that facilitates binding to DNA. We suggest the possibility that this phenomenon may be extrapolated to other ribonucleases.
authors: School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Xiao
authors: X
authors: Ge
authors: School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Xiang
authors: X
authors: Zhao
authors: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors: Akihisa
authors: A
authors: Nakagawa
authors: School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Xinqi
authors: X
authors: Gong
authors: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors: Riley Robert
authors: RR
authors: Skeen-Gaar
authors: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors: Yong
authors: Y
authors: Shi
authors: School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Haipeng
authors: H
authors: Gong
authors: School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Xinquan
authors: X
authors: Wang
authors: 1] School of Life Sciences, Tsinghua University, Beijing 100084, China [2] Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors: Ding
authors: D
authors: Xue
mesh_terms: D000818:Animals; D017209:Apoptosis; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D003851:Deoxyribonucleases / Q000378:metabolism*; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D043244:Ribonuclease III / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D004247:DNA; D003851:Deoxyribonucleases; D043244:Ribonuclease III; C019328:deoxyribonuclease A; D020169:Caspases