THE ADC LOCUS, WHICH AFFECTS COMPETENCE FOR GENETIC-TRANSFORMATION INSTREPTOCOCCUS-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 transformatio n in Streptococcus pneumoniae, a library of potential mutants has been generated by random insertion of an erythromycin resistance gene. Tra nsformation-deficient mutants were screened using an in situ colony tr ansformation test. The adc locus, which was identified in this search, was cloned and sequenced. Sequence analysis revealed a putative opero n of three ORFs (adcC, adcB and adcA) with homology to ATP-binding cas sette (ABC) transport operons encoding streptococcal adhesins such as ScaA of S. gordonii and FimA of S. parasanguis. adcA can encode a lipo protein of 313 amino acid residues containing a putative metal-binding she. The polypeptide shows about 30% sequence identity with ScaA and FimA. We discuss evidence which leads us to propose that AdcA, togethe r with a set of 14 proteins including ScaA, FimA and homologous adhesi ns, defines a new family of external solute-binding proteins, duster 9 , specific for metals.