ATP-binding (A) component of a common energy-coupling factor (ECF) ABC-transporter complex. Unlike classic ABC transporters this ECF transporter provides the energy necessary to transport a number of different substrates (Probable). Expression of the complex plus RibU in E.coli allows riboflavin uptake; uptake does not occur in the absence of RibU or the EcfA1A2T complex. Forms a heterodimer with EcfA1. Forms a stable energy-coupling factor (ECF) transporter complex composed of 2 membrane-embedded substrate-binding proteins (S component, RibU, BioY), 2 ATP-binding proteins (A component) and 2 transmembrane proteins (T component) upon coexpression in E.coli. Stable subcomplexes with both A plus T components can also be isolated. This complex interacts with at least 2 substrate-specific components, BioY and RibU. Structure 4HLU is probably in the open state. Belongs to the ABC transporter superfamily. Energy-coupling factor EcfA family.