IscB proteins are putative nucleases encoded in a distinct family of IS200/IS605 transposons and are likely ancestors of the RNA-guided endonuclease Cas9, but the functions of IscB and its interactions with any RNA remain uncharacterized. Using evolutionary analysis, RNA sequencing, and biochemical experiments, we reconstructed the evolution of CRISPR-Cas9 systems from IS200/IS605 transposons. We found that IscB uses a single noncoding RNA for RNA-guided cleavage of double-stranded DNA and can be harnessed for genome editing in human cells. We also demonstrate the RNA-guided nuclease activity of TnpB, another IS200/IS605 transposon-encoded protein and the likely ancestor of Cas12 endonucleases. This work reveals a widespread class of transposon-encoded RNA-guided nucleases, which we name OMEGA (obligate mobile element–guided activity), with strong potential for developing as biotechnologies.
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Human and bacterial TatD enzymes exhibit apurinic/apyrimidinic (AP) endonuclease activity
TatD enzymes are evolutionarily conserved deoxyribonucleases associated with DNA repair, apoptosis, development, and parasite virulence. Three TatD paralogs exist in humans, but their nuclease functions are unknown. Here, we describe the nuclease activities of two of the three human TatD paralogs, TATDN1 and TATDN3, which represent two phylogenetically distinct clades based on unique active site motifs. We found that in addition to 3′-5′ exonuclease activity associated with other TatD proteins, both TATDN1 and TATDN3 exhibited apurinic/apyrimidinic (AP) endonuclease activity. The AP endonuclease activity was observed only in double-stranded DNA, whereas exonuclease activity was operative primarily in single-stranded DNA. Both nuclease activities were observed in the presence of Mg2+ or Mn2+, and we identified several divalent metal cofactors that inhibited exonuclease and supported AP endonuclease activity. Biochemical analysis and a crystal structure of TATDN1 bound to 2′-deoxyadenosine 5′-monophosphate in the active site are consistent with two-metal ion catalysis, and we identify several residues that differentiate nuclease activities in the two proteins. In addition, we show that the three Escherichia coli TatD paralogs are also AP endonucleases, indicating that this activity is conserved across evolution. Together, these results indicate that TatD enzymes constitute a family of ancient AP endonucleases.
more » « less- Award ID(s):
- 1928918
- NSF-PAR ID:
- 10400636
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Nucleic Acids Research
- Volume:
- 51
- Issue:
- 6
- ISSN:
- 0305-1048
- Format(s):
- Medium: X Size: p. 2838-2849
- Size(s):
- p. 2838-2849
- Sponsoring Org:
- National Science Foundation
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