Graphical representation of the sporulation-proficient suppressor mutations in Rho from <i>B</i>. <i>subtilis</i> Rho⁺ strain.

The primary sequence of B. subtilis Rho subunit is shown (NP_391589.2). The major characteristic motifs identified previously by studies of different Rho proteins [177, 178] are boxed and highlighted in grey. The amino acid substitutions identified in Rho+ suppressors are marked in red. Three point mutations might have drastic effect on Rho activity. Replacement of glycine by arginine at the positions 286 and 287 (G286R and G287R, respectively) could destroy the highly conserved Q-loop forming a secondary RNA binding site, while the substitution of alanine177 localized within one of the Walker motifs by threonine (A177T; isolated twice) could affect ATP binding. Indeed, as shown in a complementation assay (S2 Table), suppressor mutations G287R, G286R and A177T completely inactivate Rho protein, while N274H (isolated twice) and P335R mutant proteins remain partially active. Two mutant Rho proteins were truncated by a stop codon at the position 146 (Q146Stop). (TIF)