Suppression of a cold-sensitive mutation in 16S rRNA by overexpression of a novel ribosome-binding factor, RbfA.

A novel 15-kDa protein, RbfA, has been identified by virtue of its ability to act as a high copy suppressor of a previously characterized dominant cold-sensitive mutation (C23U) in 16S rRNA. RbfA is found associated with free 30S ribosomal subunits, but not with 70S ribosomes or polysomes, and is essential for maximal cell growth, particularly at low temperatures. Cells lacking RbfA in a wild-type rRNA background exhibit a cold-sensitive phenotype that is strikingly similar to that of the cold-sensitive C23U rRNA mutant. The observed patterns of allele specificity of suppression and synthetic lethality in cells containing an RbfA knockout in combination with various 16S rRNA mutations suggests that RbfA interacts with the 5'-terminal helix region of 16S rRNA, possibly during a late step of 30S maturation.