This family includes the Haemophilus influenzae opacity-associated protein. This protein is required for efficient nasopharyngeal mucosal colonisation, and its expression is associated with a distinctive transparent colony phenotype. OapA is thought to be a secreted protein, and its expression exhibits high-frequency phase variation. This motif occurs at the N-terminus of these proteins. It contains a conserved histidine followed by a run of hydrophobic residues.