Table 3 Input domains found in Azospirillum sensing HKs

HK type^a

ClaHK

HyHK

ClaHK

HyHK

ClaHK

HyHK

ClaHK

HyHK

Abundant input domains

PAS / PAC

43

42 / 1

35

35 / 3

46

71

35

71

Small molecules, ions, gases, light, and redox state sensing

HAMP

12

18

18

9

14

11

11

13

Signal transduction

Uncommon input domains

GAF

3

4

3

4

7

4

5

4

Redox or oxygen sensing; cGMP binding

PHY

1

-

1

1

1

1

1

1

Tetrapyrroles; light-sensing

CHASE

3

-

2

-

3

-

2

-

Small molecules recognition

MASE

1

1

2

-

1

-

1

1

Membrane associated sensor

2CSK_N

1

-

3

-

1

-

1

-

Unknown; commonly found in N-terminal parts of HK

Cache

-

4

-

4

2

3

-

-

Small molecules recognition

MHYT

-

2

-

3

-

-

-

2

Putatively involved in metal sensing

cNMP_binding

1

-

1

-

-

-

-

-

Cyclic nucleotide monophosphate-binding

S_TKc

1

-

1

-

-

-

-

-

Serine/Threonine kinase catalytic domain

SBP_bac_1

1

-

1

-

-

-

1

-

Bacterial extracellular solute binding protein

CheB methylesterase

-

-

1

2

-

-

-

-

Chemotaxis

MeTRC

-

-

1

2

-

-

-

-

Methyl transferase

NIT

-

-

1

-

-

-

-

-

Nitrate and nitrite responsive

PBPb

-

-

-

-

1

-

1

-

High-affinity periplasmic solute-binding protein