PEPTIDE PERMEASES MODULATE TRANSFORMATION IN STREPTOCOCCUS-PNEUMONIAE

To identify elements participating in the process of transformation, a bank of genetically altered mutants of Streptococcus pneumoniae with defects in exported proteins was assessed for a decrease in transforma tion efficiency. One mutant consistently transformed 10-fold less than the parent strain. Sequence analysis and reconstitution of the altere d locus revealed a gene, plpA (permease-like protein), which encodes a putative substrate-binding protein belonging to the family of bacteri al permeases responsible for peptide transport. The derived amino acid sequence for this gene was 80% similar to AmiA, a peptide-binding pro tein homologue from pneumococcus, and 50% similar over 230 amino acids to Spo0KA which is a regulatory element in the process of transformat ion and sporulation in Bacillus subtilis. PlpA fusions to alkaline pho sphatase (PhoA) were shown to be membrane associated and labelled with [H-3]-palmitic acid, which probably serves as a membrane anchor. Expe riments designed to define the roles of the plpA and ami determinants in the process of transformation showed that: (i) mutants with defects in plpA were >90% transformation deficient while ami mutants exhibite d up to a fourfold increase in transformation efficiency; (ii) compare d to the parental strain, the onset of competence in an ami mutant occ urred earlier in logarithmic growth, whereas the onset was delayed in a plpA mutant; and (iii) the plpA mutation decreases the expression of a competence-regulated locus. Since the permease mutants would fail t o bind specific ligands, it seems likely that the substrate-permease i nteraction modulates the process of transformation.