The mI~NA levels of ATPase/5, ATPase 6, cytochrome oxidase (COX) Vlb and COX I subunit~ were found to be 2.4~13.8-fold higher in brown adipose tissue (BAT) than in heart, skeletal muscle, brain and liver of mice. The comparison with tissue contents of ATPase and COX revealed that the sele~=tive, 5-1 l-fold reduction of ATPase in BAT is not caused by decreased transcription of ATPase genes. Likewise, the ATPase ]~ and COX Vlb mRNA levels in cultured brown adipocytes were also not influenced by norepinephrine, which activated the expression of the UCP gene by two orders of magnitude. The results indicate that the biosynthesis of mitochondrial ATPase in BAT is post-transcriptionally regulatm~l. lional events are responsible for the selective reduction of the ATPase content in BAT. MATERIALS AND METHODSFour-week-old mice of Balb/c outbred strain were maintained at room temperature, on a 12 h light/12 h dark cycle. When indicated, animals were exposed to 4°C prior to use. The animals were killed by decapitation and ti.ssue samples for RNA isolation were frozen in liquid nitrogen. For other assays, 5~ homog~.:ates [w/v) were prepared in 0.25 M sucrose, 10 mM Tris/HCI, I mM EDTA, pH 7.4, and filtered through a 250/Jm nylon screen.The stromal-vascular ceils from BAT were isolated and cultivated as previously [71. Experiments were performed with cells cultured for 7 days.Total RNA was isolated as described in [8] and checked for purity and integrity. For Northern blot analysis, 20Mg RNA aliqnots were denatured in the presence of glyoxaL separated by eleetrophoresis in 1.2% agaros¢ gel and transferred to a nylon membrane (Hybond-N, Amersham) according to standard procedures [9]. Hybridization was carried out overnight at 68°C in 5x Dcnhardt's solution, 5x SSC, 50 mM sodium phosphate, pH 6.5. 0. !% SDS and 250 pg/ml of herring sperm DNA. Blots were washed in 2× SSC, 0.1 ~b SDS (2x |5 min, room temp.) and 0.Ix SSC, 0.1% SDS (2× 15 rain, 55°C). Following autoradiography the blots were stripped for 60 rain at 95~C in 0. I SDS and sequentially re-hybridized with several DNA pr3bes.The eDNA probes were generously provided by the following investigators: 1.26 kb E.coR! fragment of the rat ATPase /~-subunR eDNA in pUCI9

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