Characterization of two cDNA clones encoding isozymes of the F1F0-ATPase inhibitor protein of rice mitochondria

Two cDNA clones encoding F1F0-ATPase inhibitor proteins, which are loosely associated with the F-1 part of the mitochondrial F1F0-ATPase, were characterized from rice (Oryza sativa L. cv. Nipponbare). A Northern hybridization showed that the two genes (designated as IF1-1 and IF1-2) are transcribed in all the organs examined. However, the steady-state mRNA levels varied among organs. A comparison of the deduced amino acid sequences of the two IF1 genes and the amino acid sequence of the mature IF1 protein from potato revealed that IF1-1 and IFI-2 have N-terminal extensions with features that are characteristic of a mitochondrial targeting signal. To determine the subcellular localization of the gene products, the IF1-1 or IF1-2 proteins were fused in frame to the green fluorescent protein (GFP) or the fused GFP-beta-glucuronidase, and expressed transiently in onion or dayflower epidermal cells. Localized fluorescence was detected in mitochondria. confirming that the two IF1 proteins are targeted to mitochondria.