Mutant residues suppressing rho(0)-lethality in Kluyveromyces lactis occurat contact sites between subunits of F-1-ATPase

Characterisation of 35 Kluyveromces lactis strains lacking mitochondrial DN A has shown that mutations suppressing rho(0)- lethality are limited to the ATP1, 2 and 3 genes coding for the alpha-, beta- and gamma- subunits of mi tochondrial F-1 -ATPase. All arp mutations reduce growth on glucose and thr ee alleles, atpI-2, 1-3 and atp3-1, produce a respiratory deficient phenoty pe that indicates a drop in efficiency of the F1F0-ATP synthase complex. AT Pase activity is needed for suppression as a double mutant containing an at p allele, together with a mutation abolishing catalytic activity, does not suppress rho(0)-lethality. Positioning of the seven amino acids subject to mutation on the bovine F-1-ATPase structure shows that two residues are fou nd in a membrane proximal region while five amino acids occur at a region s uggested to be a molecular bearing. The intriguing juxtaposition of mutable amino acids to other residues subject to change suggests that mutations af fect subunit interactions and alter the properties of Fl in a manner yet to be determined. An explanation for suppressor activity of ntp mutations is discussed in the context of a possible role for F1-ATPase in the maintenanc e of mitochondrial inner membrane potential. (C) 2000 Elsevier Science B.V. All rights reserved.