Atp11p (Atpaf1p; F-1-ATPase assembly factor 1) and Atp12p (Atpaf2p; F-1-ATPase assembly factor 2) are proteins required for the assembly of beta (F-1-beta) and alpha (F-1-alpha) subunits into the mitochondrial ATPase. Here we report about 100 times lower levels of ATPAF1 and ATPAF2 transcripts in relation to the mRNA levels of F-1-alpha and F-1-beta in a range of mouse tissues. Quantitative reverse-transcription polymerase chain reaction revealed nearly constant ATPAF1 expression in all tissues in both adult and 5-day-old mice (up to two-fold differences), indicating that ATPAF1 rather behaves like a maintenance gene. In contrast, ATPAF2 expression differed up to 30-fold in the tissues analysed. ATPAF2 tissue-specific expression was also found to correlate well with mRNA levels of both F-1-alpha and F-1-beta (BATmuch greater thankidney, liver>heart, brain> skeletal muscle), showing the highest mRNA level in the thermogenic, ATPase-poor brown adipose tissue, which is characterised by a 10-fold decrease in ATPase/respiratory chain stoichiometry relative to the other tissues. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.