Table 1.

Sequences of (HhH)₂ proteins and precursor polypeptides

Construct name	Sequence*	Length, no. of residues†	Internal symmetry, %	Amino acid types
Contemporary (HhH)2 proteins‡	Representative sequences from the UvrC, PolX, RuvA, and ComEA families§	63 ± 3	21 ± 8	16 ± 1
Ancestor-(HhH)2	HRKRRSKRTLRSELDDIPGIGPKTAKALLKHFGSVE	64	46	15
	KIKKASVEELTEVPGIGPKLAKKIYEHF
Symmetric-(HhH)2	KIKKASVEELTEVPGIGPKLAKKIYEHFGSVE	60	100	13
	KIKKASVEELTEVPGIGPKLAKKIYEHF
Primordial-(HhH)2-Arg	RIRRASVEELTEVPGIGPRLARRILERLASIE	60	100	10
	RIRRASVEELTEVPGIGPRLARRILERL
Primordial-(HhH)2-Orn	OIOOASVEELTEVPGIGPOLAOOILEOLASIE	60	100	10
	OIOOASVEELTEVPGIGPOLAOOILEOL
Precursor-Arg	RIRRASVEELTEVPGIGPRLARRILERLA	29	—	10
Precursor-Orn	OIOOASVEELTEVPGIGPOLAOOILEOLA	29	—	10

^*The conserved PGIGP motif is shown in bold and the four-residue linker that joins two HhH subdomains is shown in italics. The single-letter amino acid code for ornithine is taken to be O.

^†The specified length relates to chemically synthesized variants. Protein variants expressed in E. coli include C-terminal linker (LE) and 6xHis tag (SI Appendix, Table S2).

^‡Parameters describing these proteins are reported as mean ± standard deviation.

^§Dataset S1.