ybjN was isolated as a multicopy suppressor of the temperature-sensitive coaA1 (pantothenate kinase L236F) allele of the E. coli ts9 strain, and also suppresses coaA14, coaA15 and ilu-1, which led the authors to propose a general protein-stabilizer role. All of this is over-expression evidence; no holdase or stabilizer activity has been assayed directly.

The proposed stabilizer function is an inference from suppression of several unrelated temperature-sensitive alleles, not a measured activity.

YbjN negatively regulates type 1 fimbriation: the deletion makes about three times more fimbriae by TEM with fimD up 8-fold, while multicopy ybjN abolishes pili and drops fimD 12-fold.

YbjN suppresses swimming motility and the flagellar regulon; the deletion migrates further on soft agar and induces fliA, flgB, flgD, flgE, fliL and fliM.

YbjN suppresses biofilm formation on PVC: the deletion forms about 3-fold more biofilm by crystal violet staining and multicopy ybjN about half.

YbjN suppresses colanic acid capsule production; the deletion is mucoid on high-salt LB and multicopy ybjN suppresses even the constitutive mucoidy of ackA and ackA/rcsC mutants.

Growth is unaffected by deleting ybjN and is slowed only by multicopy over-expression, so the growth effect is a gene-dosage phenomenon and not a loss-of-function phenotype.

Acid susceptibility is likewise an over-expression-only phenotype: all three strains survive equally at pH 7 and only the multicopy strain is killed at pH 2.5.

The authors' own synthesis is that YbjN acts on bacterial surface appendages as a group, which is the level at which the accepted annotations sit.

The Erwinia amylovora ortholog amyR/ybjN is likewise a negative regulator of exopolysaccharide production, with an eight-fold rise in amylovoran in the knockout, which corroborates the sign of the E. coli capsule phenotype.

This genome-scale yeast two-hybrid screen is the source of the YbjN-YpjF (Q46953) interaction behind the IntAct protein binding row. The cached full text does not name either protein; the pair appears in the screen's interaction tables and is recorded in UniProt as three experiments.

ybjN was identified by TraDIS as needed for survival of high-dose ionizing radiation and validated with a clean deletion and survival curves, falling into the mildest validated class (under about one log loss at 2,000 Gy).

The authors note the family's structural resemblance to Deinococcus DR1245 and to type III secretion chaperones, and read YbjN as having a broad stress-survival role rather than a radiation-specific one.

The only structure of the YbjN family from an enterobacterium, the Erwinia amylovora ortholog AmyR, is a homodimer with a class I type III secretion chaperone-like fold, with no evidence of a secretion role.

The authors read the fold as a protein-protein interaction module rather than an enzyme, which is consistent with YbjN carrying no catalytic motif and with the absence of any assigned molecular function.

In avian pathogenic E. coli, disrupting the adhesin fdeC raises motility, which the authors attribute to down-regulation of YbjN, corroborating the motility direction outside K-12.

UniProt has no function annotation for YbjN; the entry name is "Uncharacterized protein YbjN" and the only curated comment is the YpjF interaction.

Family assignment is to the YbjN family alone (Pfam PF10722, InterPro IPR019660 "Put_sensory_transdc_reg_YbjN"), with no domain that implies a catalytic activity.