Journal of Bioenergetics and Biomembranes, Vol. 23, No. 2, 1991 Genes Coding for Cytochrome c Oxidase in Paracoccus denitrificans John van der Oost, l Tuomas Haltia, 2 Mirja Raitio, 2 and Matti Saraste 1 Received August 28, 1990 Abstract Several loci on the Paracoccus denitrificans chromosome are involved in the synthesis of cytochrome c oxidase. So far three genetic loci have been isolated. One of them contains the structural genes of subunits II and III, as well as two regulatory genes which probably code for oxidase-specific assembly factors. In addition, two distinct genes for subunit I have been cloned, one of which is located adjacent to the cytochrome c»50gene. An alignment of six promoter regions reveals only short common sequences. Key Words: P. denitrificans, cytochrome c oxidase, mitochondria. lntroduction Bioenergetics of Paracoccus denitrißcans has been a popular object of study since the discovery that its aerobic electron transfer pathway very rauch resembles the mitochondrial respiratory chain (John and Whatley, 1975), hut its respiratory system has typical bacterial characteristics as well. For instance, multiple alternative oxidases are expressed in response to environ- mental conditions (Ludwig, 1987; Bosma et al., 1987a,b; Bosma, 1989). However, the caption that P. denitrificans is a "free-living mitochondrion" has gained new strength through detailed comparison of its respiratory enzymes to their mitochondrial counterparts. Here cytochrome c oxidase is a strikingly good example. Over the past two decades an impressive amount of physiological, biochemical, and biophysical information has accumulated on the cytochrome ~EMBL, Meyerhofstrasse 1, D-6900 Heidelberg, Germany. 2Department of Medical Chemistry, University of Helsinki, Siltavuorenpenger 10, SF-00170 Helsinki, Finland. 257 0145-479X/91/0400-0257506.50/0© 1991 Plenum Publishing Corporation