The adc locus, which affects competence for genetic transformation in Streptococcus pneumoniae, encodes an ABC transporter with a putative lipoprotein homologous to a family of streptococcal adhesins.

To identify new components involved in the phenomenon of transformation in Streptococcus pneumoniae, a library of potential mutants has been generated by random insertion of an erythromycin resistance gene. Transformation-deficient mutants were screened using an in situ colony transformation test. The adc locus, which was identified in this search, was cloned and sequenced. Sequence analysis revealed a putative operon of three ORFs (adcC, adcB and adcA) with homology to ATP-binding cassette (ABC) transport operons encoding streptococcal adhesins such as ScaA of S. gordonii and FimA of S. parasanguis. adcA can encode a lipoprotein of 313 amino acid residues containing a putative metal-binding site. The polypeptide shows about 30% sequence identity with ScaA and FimA. We discuss evidence which leads us to propose that AdcA, together with a set of 14 proteins including ScaA, FimA and homologous adhesins, defines a new family of external solute-binding proteins, cluster 9, specific for metals.