FB2026_03 , released September 17, 2026
Physical Interaction report
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General Information
Interaction Type
physical association
Interacting Genes
piwi, papi
FlyBase ID
FBig0000108303
Interaction Network
Interactions Browser links
piwi network
papi network
Reported Interactions
FBrf0213491-1.Y2H
Reference
Liu et al., 2011
Description
physical association
Assay
Collection
Source/Stage
ovary / femaleadult stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
piwi 

PIWI

bait

fused to LexA DNA-binding domain

piwi 
papi 

CG7082

prey

fused to B42 activation domain

Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
piwi 
N-terminal region
sufficient binding region
aa 1-491

coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was yeast cell line; bait produced as transgenic fusion protein; prey produced as transgenic fusion protein (prey from ovarian cDNA expression library).

(Liu et al., 2011)

115 clones of papi recovered from 212 strong positives in this piwi two hybrid screen.

(Liu et al., 2011)

Two-hybrid system: yeast LexA-BD/B42-AD

(Liu et al., 2011)
FBrf0213491-12.coIP.WB
Reference
Liu et al., 2011
Description
physical association
Assay
Collection
Source/Stage
organism / embryonic stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

PAPI

bait
piwi 

PIWI

prey
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was embryos of wild-type fly line; bait produced from endogenous gene; prey produced from endogenous gene.

(Liu et al., 2011)
FBrf0213491-2.Y2H
Reference
Liu et al., 2011
Description
physical association
Assay
Collection
Source/Stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
piwi 

PIWI

bait

fused to LexA DNA-binding domain

piwi 
piwi 
papi 

PAPI

prey

fused to B42 activation domain

papi 
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
C-terminal region
sufficient binding region
aa 257-576

coordinates relative to papi-PA

piwi 
N-terminal region
sufficient binding region
aa 1-257

coordinates relative to piwi-PA

piwi 
symmetric dimethylation sites R7 and R9
sufficient binding region
aa 7-9

"MUT" construct (R7K + R9K), coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was yeast cell line; bait produced as transgenic fusion protein; prey produced as transgenic fusion protein (prey was previously cloned reagent).

(Liu et al., 2011)

Two-hybrid system: yeast LexA-BD/B42-AD

(Liu et al., 2011)
FBrf0238516-1.coIP.WB
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
S2-unspecified
Participants
Corresponds to
Reported as
Role
Note
piwi 

Piwi

bait

Myc tag

piwi 
piwi 
papi 

Papi

prey

FLAG tag

Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
piwi 
N-terminal domain
sufficient binding region
aa 1-94

coordinates relative to piwi-PA

piwi 
N-terminal domain
necessary binding region
aa 1-94

coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was cell extract of S2 cell line; bait produced from transfected construct; prey produced from transfected construct.

(Zhang et al., 2018)
FBrf0238516-2.coIP.WB
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
S2-unspecified
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait

FLAG tag

papi 
piwi 

Piwi

prey

Myc tag

Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was cell extract of S2 cell line; bait produced from transfected construct; prey produced from transfected construct.

(Zhang et al., 2018)
FBrf0238516-3.PD.MW
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait

GST tag

papi 
piwi 

Piwi

prey

His, Strep tag

piwi 
piwi 
piwi 
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

piwi 
N-terminal domain
sufficient binding region
aa 1-94

coordinates relative to piwi-PA

piwi 
N-terminal domain residues 7,9,10,11
mutation disrupting interaction
aa 7,9,10,11

RGRRR to KGKKK, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 10
mutation disrupting interaction
aa 10

R10A or R10K, coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Interaction in vitro; bait produced as a recombinant fusion protein in bacterial system; prey produced as a recombinant fusion protein in bacterial system.

(Zhang et al., 2018)
FBrf0238516-4.ITC
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait
papi 
papi 
papi 
papi 
papi 
papi 
papi 
papi 
papi 
papi 
papi 
papi 
piwi 

Piwi

prey
piwi 
piwi 
piwi 
piwi 
piwi 
piwi 
piwi 
piwi 
piwi 
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

papi 
eTud domain residue 321
mutation decreasing interaction
aa 321

F321A, coordinates relative to papi-PA, decrease in context of binding to methylated piwi, no difference in binding to unmethylated piwi.

papi 
eTud domain residue 328
mutation decreasing interaction
aa 328

Y328A, coordinates relative to papi-PA

papi 
eTud domain residue 351
mutation decreasing interaction
aa 351

F351A, coordinates relative to papi-PA

papi 
eTud domain residue 354
mutation decreasing interaction
aa 354

Y354A, coordinates relative to papi-PA

papi 
eTud domain residue 356
mutation decreasing interaction
aa 356

D356A, coordinates relative to papi-PA

papi 
eTud domain residue 348
mutation decreasing interaction
aa 348

D348A, coordinates relative to papi-PA

papi 
eTud domain residue 359
mutation decreasing interaction
aa 359

Y359A, coordinates relative to papi-PA

papi 
eTud domain residues 348,359
mutation disrupting interaction
aa 348,359

D348A,Y359A, coordinates relative to papi-PA

papi 
eTud domain residue 407
mutation decreasing interaction
aa 407

E407A, coordinates relative to papi-PA

papi 
eTud domain residue 323
mutation decreasing interaction
aa 323

F323A, coordinates relative to papi-PA, decrease in context of binding to methylated piwi, no difference in binding to unmethylated piwi.

papi 
eTud domain residue 358
mutation decreasing interaction
aa 358

E358A, coordinates relative to papi-PA

piwi 
N-terminal domain
sufficient binding region
aa 4-14

coordinates relative to piwi-PA

piwi 
N-terminal domain residue 7
mutation decreasing interaction
aa 7

R7A or R7K, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 9
mutation decreasing interaction
aa 9

R9A or R9K, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 11
mutation decreasing interaction
aa 11

R11A or R11K, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 8
mutation decreasing interaction
aa 8

G8V, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 10
mutation disrupting interaction
aa 10

R10A, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 10
mutation decreasing interaction
aa 10

R10K, coordinates relative to piwi-PA

piwi 
N-terminal domain residue 5
mutation decreasing interaction
aa 5

Q5A, coordinates relative to piwi-PA

piwi 
N-terminal domain residues 7,9,10,11
mutation disrupting interaction
aa 7,9,10,11

RGRRR to KGKKK, coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Interaction in vitro; bait produced as a recombinant fusion protein in bacterial system; prey peptides were commercially synthesized.

(Zhang et al., 2018)

Kd=0.57uM for unmethylated piwi. Methylation at piwi R7, R9, R11 decreased binding affinity, while R10 methylation increased binding affinity to 0.057uM.

(Zhang et al., 2018)
FBrf0238516-5.XC
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

neutral component
papi 

Papi

neutral component
papi 
papi 

Papi

neutral component
papi 
piwi 

Piwi

neutral component
piwi 
piwi 

Piwi

neutral component
piwi 

Piwi

neutral component
piwi 
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

piwi 
N-terminal domain
sufficient binding region
aa 4-14

coordinates relative to piwi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Interaction in vitro; bait produced as a recombinant fusion protein in bacterial system; prey peptide was commercially synthesized.

(Zhang et al., 2018)

Since initial attempts to co-crystallize piwi and papi were unsuccessful, a D287A mutant (papi to reduce potential surface entropy) and the higher affinity R10 methylated piwi peptide were used in crystallization. The crystal structure of papi with unmethylated piwi was also determined.

(Zhang et al., 2018)
FBrf0238516-6.coIP.WB
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
Cell line used
S2-unspecified
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait

FLAG tag

papi 
papi 
piwi 

Piwi

prey

Myc tag

Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain residue 328
mutation decreasing interaction
aa 328

Y328A, coordinates relative to papi-PA

papi 
eTud domain residue 348
mutation decreasing interaction
aa 348

D348A, coordinates relative to papi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Source was cell extract of S2 cell line; bait produced from transfected construct; prey produced from transfected construct.

(Zhang et al., 2018)
FBrf0238516-7.PD.MS
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
ovary / femaleadult stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait

GST tag

papi 
piwi 

Piwi

prey
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

Interaction in vitro; bait produced as a recombinant fusion protein in bacterial system; prey derived from wild-type ovary extract.

(Zhang et al., 2018)
FBrf0238516-8.PD.WB
Reference
Zhang et al., 2018
Description
physical association
Assay
Collection
Source/Stage
ovary / femaleadult stage
Cell line used
Participants
Corresponds to
Reported as
Role
Note
papi 

Papi

bait

GST tag

papi 
piwi 

Piwi

prey
Experimental entities
Corresponds to
Identifier
Reported
Role
Note
Subregions with role in interaction
Corresponds to
Description
Role
Coordinates
Note
papi 
eTud domain
sufficient binding region
aa 259-479

coordinates relative to papi-PA

Isoform-specific participants
Corresponds to
Description
Role
Note
Comments concerning this interaction

The R10me2s form of piwi was detected in the papi pull-down.

(Zhang et al., 2018)

Interaction in vitro; bait produced as a recombinant fusion protein in bacterial system; prey derived from wild-type ovary extract.

(Zhang et al., 2018)
External Crossreferences and Linkouts ( 1 )
Linkouts
MIST - An integrated Molecular Interaction Database
References (2)