The invention provides isolated nucleic acid molecules, designated PGC-1.beta. nucleic acid molecules, which encode novel PGC-1 related coactivator molecules. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing PGC-1.beta. nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a PGC-1.beta. gene has been introduced or disrupted. The invention still further provides isolated PGC-1.beta. proteins, fusion proteins, antigenic peptides and anti-PGC-1.beta. antibodies. Diagnostic and therapeutic methods utilizing compositions of the invention are also provided.