Table 1.
G4-quadruplex binding proteins (G4BPs)
| G4-sequence | Function, if known | Comments | |
|---|---|---|---|
| Telomeric G4BPs | |||
| POT1 | (TTAGGG)n | Unfolding of G4 (and refolding with POT1-TPP1 complex | Selective to anti-parallel G4Qs |
| RPA | (TTAGGG)n | Unfolds G4Qs | Unfolds both parallel and anti-parallel G4Qs |
| Human CST | TTAGGG.AATCCC | Unfolds G4Qs | Complex of 3 proteins; CTC1 contains the DNA-binding site |
| hnRNP A1 and UP1 | (TTAGGG)n | Unfolds G4Qs |
Specifically, nYAGn seq Binds RNA and DNA |
| BLM | (TTAGGG)n | Unfolds G4Qs (leading strand) in 3′-5′ |
Needs a ssDNA spacer between G4Q and the replication fork to function Similar to WRN |
| WRN | (TTAGGG)n | Unfolds G4Qs (lagging strand) in 3′-5′ | Similar to BLM |
| BRCA1 | (TTAGGG)n | Binds G4Qs in vitro | |
| Pif1 | (TTAGGG)n | Unfolds 5′-3′ direction | |
| Replication G4BPs | |||
| FANCJ | Unfolds G4Qs in 5′-3′ direction | unwinds both intramolecular and intermolecular G4Qs | |
| Promoter G4BPs | |||
| Sp1 |
G4 (C) G3 (CC) G5 (C) G4 (TCCCGGC) G4 (CGG) (VEGF) CCCGGGCGGGCGCGAGGGAGGGGAGG (c-KIT) CGGGGCGGGGCGGGGGCGGGGGCG (HRAS) |
Binds parallel and antiparallel G4Qs | |
| DHX36 | Many sequences | Unfolds G4Qs in 3′-5′ | Strong preference for binding parallel DNA and RNA G4Qs over antiparallel; requires trailing 3′ end |
| Nucleolin |
TGGGGAGGGTGGGGAGGGTGGGGAAGG (c-MYC) (GGGGCC)n (HRE) |
Stabilizes G4Q to suppress transcription | Preferentially binds parallel G4Qs but can bind both |
| NM23-H2 | TGGGGAGGGTGGGGAGGGTGGGGAAGG (c-MYC) | Unfolds G4Q to enable transcription | |
| MAZ |
TGGGGAGGGTGGGGAGGGTGGGGAAGG (c-MYC) ACAGGGGTGTGGGG (Pur-1) TCGGGTTGCGGGCGCAGGGCACGGGCG and CGGGGCGGGGCGGGGGCGGGGGCG (HRAS) GGGAGGGAGGGAAGGAGGGAGGGAGGGA (KRAS) |
Unfolds G4Qs to enable transcription | |
| PARP1 |
C3G3CG3CGCGAG3AG4AG2 (c-KIT) TGGGGAGGGTGGGGAGGGTGGGGAAGG (c-MYC) GGGAGGGAGGGAAGGAGGGAGGGAGGGA (KRAS) |
Recognizes parallel G4Qs; binding with c-KIT activates PARP1 | |
| XPD/XPB | XPD: 5′-3′ direction XPB: 3′-5′ direction | ||
| hnRNP |
GGGAGGGAGGGAAGGAGGGAGGGAGGGA (KRAS) GGGGTGGGGCCCTGCGAGGGCGGG (TRA2β) |
Unfolds G4Q | |
| RNA G4BPs | |||
| hnRNP A1 |
AACGAGGGAGGGAGGGAGAGGGAGAGA- (MMP16) AGCCGGGGGCUGGGCGGGGACCG GGCUUGU (ARPC2) |
Unfolds G4Q | |
| DHX36 | Many sequences | ||
| DHX9 | Many sequences | Unfolds G4Qs in 3′-5′ | Preference for RNA substrates; requires a 3′ single-stranded tail for initial binding |
| FMRP | GUGUGGAAGGAGUGGCUGGGUUG(sc1) | Stabilizes the G4Q | |