Permease that is involved in the transport across the cytoplasmic membrane of D-alanine, D-serine, glycine and beta-alanine (PubMed:4926674, PubMed:4574696, PubMed:4583203, PubMed:15221223, PubMed:23316042). Also contributes to L-alanine uptake (PubMed:4574696, PubMed:4583203). In addition, in minimal media, transports the broad spectrum antibiotic D-cycloserine into the cell (PubMed:4926674, PubMed:4574696, PubMed:23316042). Transports D-cycloserine only in minimal media, and not in a complex medium, suggesting that CycA does not play a role in D-cycloserine transport when E.coli is grown in a complex or biologically relevant medium, probably due to competition from other CycA substrates present in the medium (PubMed:23316042). D-alanine(in) + H(+)(in) = D-alanine(out) + H(+)(out) D-serine(out) + H(+)(out) = D-serine(in) + H(+)(in) glycine(in) + H(+)(in) = glycine(out) + H(+)(out) beta-alanine(in) + H(+)(in) = beta-alanine(out) + H(+)(out) H(+)(in) + L-alanine(in) = H(+)(out) + L-alanine(out) D-cycloserine(in) + H(+)(in) = D-cycloserine(out) + H(+)(out) Beta-alanine uptake is inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP), which dissipates the proton motive force. In complex media, expression is negatively regulated by Hfq and the small non-translated RNA GcvB (PubMed:19118351). Hfq is required for the GcvB effect (PubMed:19118351). Mutant exhibits increased resistance to D-cycloserine when grown in a minimal medium, but no change in D-cycloserine sensitivity compared to its parental strain when grown in a complex medium. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Amino acid transporter (AAT) (TC 2.A.3.1) family.