Copyright © by The American Society for Biochemistry and Molecular BiologyMammalian AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that acts as a sensor of cellular energy status. AMPK is a heterotrimer of three different subunits, i.e. α, β and γ, with α being the catalytic subunit and β and γ having regulatory roles. Although several studies have defined different domains in α and β involved in the interaction with the other subunits of the complex, little is known about the regions of the γ subunits involved in these interactions. To study this, we have made sequential deletions from the N-termini of the γ subunit isoforms and studied the interactions with α and β subunits, both by two hybrid analysis and by co-immunoprecipitation. Our results suggest that a conserved region of 20-25 amino acids in γ1, γ2 and γ3, immediately N-terminal to the Bateman domains, is required for the formation of a functional, active αβγ complex. This region is required for the interaction with the β subunits. The interaction between the α and γ subunits does not require this region and occurs instead within the Bateman domains of the γ subunit, although the α-γ interaction does appear to stabilize the β-γ interaction. In addition, sequential deletions from the C-termini of the γ subunits indicate that deletion of any of the CBS motifs prevents the formation of a functional complex with the α and β subunits.This study was supported by the EXGENESIS Integrated Project (LSHM-CT-2004-005272) funded by the European Commission. Studies in the PS laboratory were also supported by the Spanish Ministry of Education and Science grant SAF2005-00852. Studies in the DGH laboratory were also supported by a Programme Grant from the Wellcome Trust.Peer reviewed