Involved in the biosynthesis of actinomycin (PubMed:10212227). Acts as a carrier in the transfer and thioesterification of 4-methyl-3-hydroxyanthranilic acid (4-MHA) (PubMed:10212227). Antibiotic biosynthesis. 4'-phosphopantetheine is transferred from CoA to a specific serine of the apo-form of this carrier protein. Belongs to the acyl carrier protein (ACP) family.