The role of a repetitive DNA motif (5'-CAAT-3') in the variable expression of the Haemophilus influenzae lipopolysaccharide epitope alpha Gal(1-4)beta Gal.

Haemophilus influenzae lipopolysaccharide (LPS) contains structures, defined by monoclonal antibodies, which undergo phase variation. This investigation reports the nucleotide sequence of lic2A, which is required for the expression of at least three phase-variable LPS epitopes, one of which has the structure alpha Gal(1-4)beta Gal. lic2A contains multiple tandem repeats of the tetramer 5'-CAAT-3'. Previous studies have correlated changes in the number of 5'-CAAT-3' repeats with the phase-variable expression of the alpha Gal(1-4)beta Gal epitope. To obtain direct evidence for this, the 5'-CAAT-3' repeat region from lic2A was amplified directly from immunostained colonies and sequenced. This demonstrated that the variable expression of LPS epitopes, including alpha Gal(1-4)beta Gal, is in part directly dependent upon the number of copies of 5'-CAAT-3' within lic2A.