May be involved in an alternative pathway for phosphopantetheinyl transfer and holo-ACP synthesis in E.coli. The native apo-protein substrate is unknown. Is able to functionally replace AcpS in vivo but only when expressed at high levels. apo-[ACP] + CoA = adenosine 3',5'-bisphosphate + H(+) + holo-[ACP] Belongs to the P-Pant transferase superfamily. Gsp/Sfp/HetI/AcpT family.