Paris—Advertising holding company Publicis Groupe has bought a majority stake in U.K.-based Walker Media, as well as 100% of South African search marketing company Synergize. Financial terms of the deals were not disclosed. Publicis acquired 75% of London-based Walker Media from M&C Saatchi, which will continue to own 25% of the company. Walker will continue to operate as a separate agency in the U.K. and as part of Zenith Optimedia Group, the company said in a statement. Cape Town-based Synergize will be blended into Publicis' Saatchi & Saatchi division, which will be renamed Saatchi & Saatchi Synergize. Publicis Group is in the process of merging with Omnicom Group to form the world's largest advertising agency holding company, pending regulatory approval. When completed, the combined company will be called Publicis Omnicom Group.