Figure 2.

GreA is a major transcription proofreading factor identified by the cre/galK-loxP-INV genetic reporter assay. (A) Cells patched on MacConkey Galactose (MacGal) plates on M63Gal agar/agarose plates all show similar results that the G→A transcription error, identified by the density of Gal⁺ colonies, dramatically increases if GreA (ΔgreA cells) or both GreA and GreB (ΔgreAB cells) are deleted from the wild-type cells (greA⁺B⁺ cells). Deletion of only GreB (ΔgreB cells) has no effect. (B) Quantitation of the effect of Gre factors on the apparent frequency of G→A transcription error measured by the plating efficiency assay on M63Gal agarose. Each bar represents a value of Gal⁺ counts from nine independent cell cultures plated in duplicate with the error bars shown. (C) Patches of ΔgreA cells on M63Gal agar show that overexpression of GreB (pGreB) or GreA (pGreA) almost equally suppresses the frequency of G→A transcription error in GreA-lacking cells as compared to the same cells containing pBR322 control plasmid.