Permease that is involved in the transport across the cytoplasmic membrane of D-alanine, D-serine and glycine (PubMed:16952954, PubMed:23316042). Is the only transporter of D-alanine (PubMed:16952954). Transports D-serine less efficiently than DsdX (PubMed:16952954). In addition, in minimal media, transports the broad spectrum antibiotic D-cycloserine into the cell (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) D-cycloserine(in) + H(+)(in) = D-cycloserine(out) + H(+)(out) Uptake of D-serine is inhibited by D-alanine, D-cycloserine, glycine and at high concentrations of D-threonine. Single deletion, grows on D-serine or D-serine plus glycerol but not D-alanine. A double dsdX-cycA deletion grows in D-serine plus glycerol, but not D-serine or D-alanine alone, growth on D-serine (but not D-alanine) is restored by dsdX (PubMed:16952954). 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 or human urine (PubMed:23316042). E.coli CFT073, a uropathogenic strain (UPEC), was originally isolated from urine, which has a high concentration of D-serine. D-serine is toxic to bacteria. The abililty to take up D-serine coupled with the activity of D-serine dehydratase (dsdA) may allow use of this amino acid as a carbon source in a sugar-poor environment. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Amino acid transporter (AAT) (TC 2.A.3.1) family.