The plasma-membrane annotation on this horse record is produced by combined automated IEA pipelines (here an ARBA rule plus the UniProt subcellular-location keyword mapping), not by any equine observation, so it inherits whatever the rule conditions assert about the family.

The horse EFR3A entry is an unreviewed 796-residue TrEMBL record whose protein name is assigned by an ARBA automated annotation rule, with no equine experimental characterization.

The record's sequence begins MIDKDGLVKA after the initiator methionine; the PTRVCCCCS segment that follows the human initiator Met and contains the Cys6-Cys9 palmitoylation cluster is absent from this model.

The downstream EFR3-like ARM/HEAT repeat architecture is detected intact, which is what secures family identity independently of the missing N-terminus.

Human EFR3A is a component of the complex that localizes phosphatidylinositol 4-kinase to the plasma membrane, and within that complex it is specifically the membrane-anchoring component - so losing the anchor is losing its assigned role, not a peripheral feature.

The complex is PI4KA plus EFR3 (EFR3A or EFR3B), TTC7 (TTC7A or TTC7B) and HYCC (HYCC1 or HYCC2), giving the specific partners an equine assembly test would need to score.

Plasma-membrane residence is a lipid-anchor localization, with a small cytosolic pool also observed; palmitoylation is what anchors the protein.

Human EFR3A isoform 2 is the curated Q14156-2 product whose sequence is described by VAR_SEQ feature VSP_022217.

The VSP_022217 variant deletes residues 1-36, so this curated human isoform lacks the entire Cys6-Cys9 palmitoylation cluster and cannot be N-terminally palmitoylated.

Human UniProt flags three cDNA translations as erroneous initiations with extended N-termini, independent evidence that EFR3A start calls are error-prone at this end of the protein.

Over the paired region the horse and human proteins are near-identical (98.24% across 796 residues), with the whole horse sequence paired and roughly 25 human residues unpaired - so the difference is confined to one end rather than distributed.

The comparison explicitly declines to establish one-to-one orthology or to verify the sequence that was supplied to the prediction pipeline, so the truncation is recorded as a model limitation rather than a demonstrated equine difference.

The pairwise alignment places horse Met1 opposite human Met1 and then opens a 25-residue gap over human residues 2-26. Horse residue 2 therefore aligns to human residue 27; residue 29 is only where contiguous identity resumes after two mismatches.

Phosphatidylinositol 4-kinase III alpha reaches the plasma membrane as part of an evolutionarily conserved complex containing Efr3, which the authors identify as a palmitoylated peripheral membrane protein rather than a transmembrane one.

The N-terminal Cys-rich motif is conserved in all metazoans and was identified as the candidate palmitoylation site, which is why its absence from a mammalian EFR3A model is a specific concern rather than ordinary sequence divergence.

Palmitoylation at that motif was demonstrated by metabolic labeling, and the palmitoylation-deficient EFR3A mutant C6S/C7S/C8S/C9S relocalized to the cytosol - direct evidence that these exact residues, the ones missing from the horse model, determine plasma-membrane residence.

The equivalent EFR3B palmitoylation-deficient mutant also failed to recruit TTC7B and the kinase to the plasma membrane, showing the motif is required for the complex's function and not only for EFR3's own localization.

Mammalian Efr3, unlike fungal Efr3, is N-terminally palmitoylated, and palmitoylation is required for its plasma-membrane association.

A conserved N-terminal basic patch is also required for mammalian EFR3A plasma-membrane localization (mouse K50E/R53A/R61E/R68E/R70E mutant).

The Efr3 C-terminal region is the binding site for Ypp1/TTC7, which links Efr3 to the kinase.

EFR3 is an adaptor of the plasma-membrane PI4KIIIalpha complex together with TTC7 and FAM126A/HYCC1.

All four horse EFR3A UniProt entries derive from one Ensembl gene. A0A9L0S4L8 uses a distinct first exon (chr9:74894800-74895054) and lacks human residues 2-26 including Cys6-Cys9, whereas A0A3Q2GU27 (821 aa) is full length and retains CCCC.

The mouse EFR3A basic-patch residues mutated in PMID:24360784 are all retained in A0A9L0S4L8.