INSIGHT INTO THE INTERACTIONS BETWEEN SUBUNIT-I AND SUBUNIT-II OF THECYTOCHROME-C-OXIDASE OF THE YEAST SACCHAROMYCES-CEREVISIAE BY MEANS OF EXTRAGENIC COMPLEMENTATION

In yeast, revertants were selected from two respiratory deficient muta nts carrying mutations in the catalytic subunits of cytochrome oxidase . From a mutant carrying a double mutation in the vicinity of the copp er binding pocket in subunit II, two genetically independent revertant s were obtained in which the same extragenic reversion mutation was ob served, A147V, in the putative helix 4 of subunit I. A comparison with revertants derived from the second deficient mutant, carrying the def iciency mutation, S140L, in the loop 3-4 of subunit I, provides additi onal data in favour of an interaction between helix 4 of subunit I and subunit II.