Regulatory features of transcription in isolated mitochondria from Artemiafranciscana embryos

Optimal conditions were developed for an in organello transcriptional run-o n assay using mitochondria isolated from Artemia franciscana embryos to inv estigate potential regulatory features of RNA synthesis under conditions of anoxia-induced quiescence. Transcription is not dependent on oxidative pho sphorylation for maximal activity when exogenous ATP is available. Bona fid e transcription products, as assessed by hybridization with specific mitoch ondrial cDNAs from A. franciscana, are produced in an inhibitor-sensitive m anner. Transcription rate measured at pH 7.9 is reduced 80% when pH is lowe red to 6.3, a pH range that mimics the in vivo change seen on exposure of e mbryos to anoxia. The proton sensitivity of mitochondrial RNA synthesis may provide a mechanism to depress this significant energy expenditure during quiescence. The influence of nucleotide concentration on kinetics is compli cated by an interdependence among nucleotide species. ATP inhibition observ ed at subsaturating UTP concentrations is relieved when UTP is at saturatin g, physiologically relevant levels. Taken together, these data suggest that local (versus nuclear mediated) control is important in dictating mitochon drial transcription during rapid modulations in gene expression, such as th ose observed under anoxia-induced quiescence.