Table 1

Substrate specificity of bacterial endoribonuclease toxins

TA operon	Protein/RNA	TA	Signals/Regulators	Recognition sequence	Reference
Type II ribosome-dependent endoribonuclease toxin
relB-relE	RelE	Toxin	Amino acid or glucose starvation /Lon protease (E. coli)	cleaves mRNA at UA↓G, UA↓A stop codons, and CA↓G Gln sense codon in the ribosomal A site (E. coli)	(5, 21, 25)
	RelB	Antitoxin
yefM-yoeB	YefM	Antitoxin	Lon protease overexpression	UA↓A (stop), AAA↓ (Lys), AA↓U (Asn), AA↓A (Lys), CU↓G (Leu), GC↓G (Ala) Cleaves 3 nt downstream of the AUG initiation codon	(20, 29, 31, 32)
	YoeB	Toxin
yafN-yafO	YafN	Antitoxin	Amino acid or glucose starvation (yafN promoter), UV irradiation, SOS response (dinB promoter)	Cleaves 11-13 nt downstream of the AUG initiation codon	(8, 34)
	YafO	Toxin
dinJ-yafQ	DinJ	Antitoxin	Biofilm formation, SOS response /LexA repressor	AA↓A (Lys) A/G	(36, 38)
	YafQ	Toxin
higB-higA	HigB	Toxin	Amino acid starvation	Cleaves an adenosine-rich codon including AAA (Lys), ACA (Thr)	(8, 40-42)
	HigA	Antitoxin
prlF-yhaV	YhaV	Toxin	Unknown	Cleavage mostly occurs between codons but also occurs within codons (between the second and third bases in codons) with a low frequency	(45)
	PrIF	Antitoxin
Type II ribosome-independent endoribonuclease toxin
mazE-mazF	MazE	Antitoxin	Amino acid starvation, phage P1 infection (E. coli) development /MrpC (Myxococcus xanthus), nutrition starvation, antibiotics (Mycobacterium tuberculosis)	↓ACA (E. coli), U↓ACAU (B. subtilis), (G/A)U↓UGC (Myxococcus xanthus), U↓ACA (Deinococcus radiodurans), U↓ACAU (Staphylococcus aureus)	(6, 50-54, 92)
	MazF	Toxin
chpBI-chpBK	ChpBI	Antitoxin	Unknown	↓ACY or A↓CY (Y: A, U, G)	(57)
	ChpBK	Toxin
pemI-pemK	PemI	Antitoxin	Unknown	U↓AH or UA↓H (H: A, U, C)	(60)
	PemK	Toxin
mqsR-mqsA	MqsR	Toxin	Amino acid or glucose starvation	Mostly ↓GCU or G↓CU	(8, 62)
	MqsA	Antitoxin
hicA-hicB	HicA	Toxin	Sxy competence factor and CRP-cAMP	No specific cleavage site in mRNAs A↓AAC sequences in tmRNA	(7, 69)
	HicB	Antitoxin
Type I endoribonuclease toxin
symER	SymE (protein)	Toxin	SOS response	Not determined yet	(70)
	SymR (RNA)	Antitoxin
Type III endoribonuclease toxin
antiQ-abiQ	AbiQ	Toxin	Phage infection (Lactococcal lactis)	Adenine-rich region within the antiQ RNA sequence between 26th and 27thadenines (A↓AAA) in the 35 nt-antiQ RNA (Lactococcal lactis)	(71, 74)
	antiQ	Antitoxin
toxI-toxN	ToxN (protein)	Toxin	Phage infection (Pectobacterium atrosepticum)	AA↓AU (Pectobacterium atrosepticum) A↓AAAA (Bacillus thuringiensis)	(75, 76)
	ToxI (RNA)	Antitoxin

BMB Reports 2020;53:611-21 https://doi.org/10.5483/BMBRep.2020.53.12.203

© 2020 BMB Reports