CG32706 encodes the Drosophila member of the ABT1/Esf2 protein family, a 230-residue protein with a central RNA-recognition motif (RRM) and the conserved ABT1/Esf2 core segment that follows it. It is the fly counterpart of budding-yeast Esf2 and vertebrate ABT1 within a single PANTHER subfamily. In yeast, Esf2 is a nucleolar component of the small-subunit (SSU) processome/90S preribosome that associates with the 5' external transcribed spacer and U3 snoRNA, binds pre-rRNA, stimulates the ATPase activity of the DEAD-box helicase Dbp8, and is required for SSU-processome assembly and compaction and hence for the early pre-rRNA cleavages that generate 18S rRNA. By descent, CG32706 is expected to act in the nucleolus as an RNA-binding assembly factor of the 40S-subunit biogenesis machinery rather than as a nuclease. No biochemical or localization study of the fly protein itself has been reported; a piggyBac insertion near the 3' end of the gene increased susceptibility to Listeria monocytogenes infection with elevated bacterial load in a whole-animal screen.
Existing Annotations Review
GO Term
Evidence
Action
Reason
GO:0000447 endonucleolytic cleavage in ITS1 to separate SSU-rRNA from 5.8S rRNA and LSU-rRNA from tricistronic rRNA transcript (SSU-rRNA, 5.8S rRNA, LSU-rRNA)
IBA GO_REF:0000033
KEEP AS NON CORE
Summary: PAINT inference from node PTN000267771 to the single ABT1/Esf2 subfamily (PTHR12311:SF7) that contains CG32706 and yeast Esf2. Yeast Esf2 depletion blocks cleavage at A2 (the ITS1 site separating SSU from LSU precursors), as a consequence of failed SSU-processome assembly.
Reason: The phylogenetic placement is sound (single subfamily, one-to-one, RRM and family core intact; see bioinformatics re-review), so the IBA is retained. Esf2 is a component of the SSU processome, the particle that performs the A0-A2 cleavages, and so contributes structurally to the machinery, but it is not the endonuclease, and the yeast paper attributes the cleavage defect to failed processome assembly. The cleavage process is therefore kept as a non-core consequence of the core assembly role (GO:0034462), not as the protein's primary function.
Esf2p-depleted cells are defective for pre-rRNA processing at the early nucleolar cleavage sites A0 through A2 and consequently are inhibited for 18S rRNA synthesis.
This suggests that in the absence of proper SSU processome assembly, early pre-rRNA processing is inhibited
file:DROME/CG32706/CG32706-uniprot.txt
PANTHER; PTHR12311:SF7; ACTIVATOR OF BASAL TRANSCRIPTION 1; 1.
GO:0000472 endonucleolytic cleavage to generate mature 5'-end of SSU-rRNA from (SSU-rRNA, 5.8S rRNA, LSU-rRNA)
IBA GO_REF:0000033
KEEP AS NON CORE
Summary: PAINT inference from the ABT1/Esf2 node; yeast Esf2 is required for cleavage at site A1, which generates the mature 5' end of 18S rRNA.
Reason: Same reasoning as the other early-cleavage IBA rows. The inheritance is phylogenetically sound and Esf2 is part of the processome that performs A1 cleavage, but the protein is an assembly factor and not the nuclease, and the cleavage defect follows from the assembly defect. Retained as non-core.
Esf2p-depleted cells are defective for pre-rRNA processing at the early nucleolar cleavage sites A0 through A2 and consequently are inhibited for 18S rRNA synthesis.
file:DROME/CG32706/CG32706-uniprot.txt
PANTHER; PTHR12311:SF7; ACTIVATOR OF BASAL TRANSCRIPTION 1; 1.
GO:0000480 endonucleolytic cleavage in 5'-ETS of tricistronic rRNA transcript (SSU-rRNA, 5.8S rRNA, LSU-rRNA)
IBA GO_REF:0000033
KEEP AS NON CORE
Summary: PAINT inference from the ABT1/Esf2 node; yeast Esf2 binds the 5' ETS and is required for cleavage at site A0 in the 5' ETS.
Reason: The inheritance is phylogenetically sound and the yeast ortholog associates directly with the 5' ETS in the processome. As for the other cleavage rows, Esf2 contributes to the processing particle rather than catalysing the cut, and its demonstrated primary role is processome assembly; kept as non-core.
Summary: InterPro2GO mapping from the RNA-binding-domain superfamily. Correct but too general; the family-specific evidence supports RNA binding.
Reason: The RRM (residues 62-140) belongs to the ABT1/Esf2-specific RRM subtype, and the yeast ortholog in the same PANTHER subfamily binds pre-rRNA in vitro and associates with the 5' ETS and U3 snoRNA in vivo. The gene already carries GO:0003723 RNA binding (IBA and IEA), the specific descendant that should replace this term.
Summary: PAINT inference of RNA binding for the ABT1/Esf2 clade, grounded on yeast Esf2 experiments.
Reason: CG32706 sits in the same single PANTHER subfamily (PTHR12311:SF7) as yeast Esf2, its RRM aligns without gaps to the yeast RRM, and yeast Esf2 binds pre-rRNA fragments in vitro and the 5' ETS in vivo. RNA binding is the most precise molecular function the evidence supports; the exact RNA site is unknown even in yeast.
Summary: InterPro2GO mapping from the RRM domain; consistent with the IBA row for the same term.
Reason: An RRM-based RNA-binding call is generic, but here it is reinforced by the ABT1/Esf2 family placement and the pre-rRNA binding of the yeast ortholog, so the same claim is accepted on both rows.
Summary: PAINT inference of nucleolar activity from the ABT1/Esf2 node.
Reason: Yeast Esf2 is nucleolar and acts in 90S preribosomes, which assemble in the nucleolus; human ABT1 was found in the nucleolar proteome. The fly protein has not been localized experimentally, but nucleolar action follows from the conserved role and the sound phylogenetic placement.
Summary: UniProt subcellular-location mapping (itself from an ARBA rule); the same claim as the IBA nucleolus row.
Reason: The UniProt location line rests on an ARBA rule and is not independent evidence, but the claim is consistent with the phylogenetically grounded IBA row and the yeast ortholog's nucleolar localization, so it is accepted for consistency with that row.
Summary: PAINT inference of the core ABT1/Esf2 process; this is the best description of what the protein does.
Reason: Yeast Esf2 is itself a component of the SSU processome (5' ETS, U3 and processome proteins) and its depletion blocks processome assembly and compaction on chromatin spreads, so it participates in assembly rather than being a substrate of it. CG32706 inherits this by descent within a single, one-to-one PANTHER subfamily with an intact family core.
IMP PMID:18245331 Identification of Drosophila mutants altering defense of and...
KEEP AS NON CORE
Summary: Whole-animal forward screen; a piggyBac line (10881) inserted within 100 bp of the 3' end of CG32706 was more susceptible to Listeria monocytogenes, with increased bacterial load, and more sensitive to S. aureus.
Reason: The full text (PMC2278058, read online; not in the local cache) places the CG32706 insertion line in the defense-defect class (increased L. monocytogenes growth), which is exactly what the curator annotated, so the experimental annotation is retained. It rests on a single insertion allele without reported revertant or second-allele confirmation, and a general defect in ribosome biogenesis is a plausible indirect cause; no immune-specific activity of the protein is known. It is therefore kept as a non-core, organism-level process.
In the second group, mutants have a typical defense defect in which bacterial growth is increased and survival is decreased.
Core Functions
RNA-binding component of the nucleolar small-subunit processome that is required for processome assembly and compaction, and hence for the early pre-rRNA cleavages that produce 18S rRNA (inferred by descent from yeast Esf2 within PANTHER PTHR12311:SF7).
Q: Does CG32706 bind and stimulate the ATPase of the fly Dbp8 ortholog, as yeast Esf2 does for Dbp8? The fly protein lacks most of the yeast C-terminal region required for Dbp8 binding, and PAINT did not propagate an ATPase-activator activity to the clade.
Q: Is the increased Listeria load of the 3'-end piggyBac insertion line due to loss of CG32706 function, and if so is it a specific immune role or a general consequence of reduced ribosome biogenesis?
Suggested Experiments
Experiment: Tag CG32706 at the endogenous locus and test nucleolar localization and co-sedimentation with 90S preribosomes; RNAi or CRISPR knockdown followed by northern analysis of early pre-rRNA intermediates.
Experiment: Excise the 10881 piggyBac insertion (precise excision revertants) or generate an independent CRISPR null, and retest Listeria monocytogenes susceptibility and bacterial load.
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
The ProtNLM2 API snapshot retrieved 2026-09-08 contains no GO-term predictions for Q8IRM9. RNA binding (GO:0003723) and small-subunit processome assembly (GO:0034462) are supported omission candidates: the target has the specific ABT1/Esf2 family assignment and retained RNA-recognition motif, existing PAINT/IBA annotations, and a characterized yeast Esf2 homolog that binds pre-rRNA and supports processome assembly. This is a conserved family inference, not a direct fly biochemical assay. The separate FUNCTION paragraph has CNN judgments for the broad processome/18S-rRNA claims and for the A0/A1/A2 cleavage-site claims, which GOA carries for this gene by IBA (GO:0000480, GO:0000472, GO:0000447) and the gene review keeps. No intrinsic nuclease activity is inferred. This completed record assesses the absence of GO output; predictions is empty because no GO or EC prediction was emitted. The narrative assessments remain in the linked function review and are not scores assigned to the omission.