Fig. 1. Transcriptional activity of the CHA1 gene in cells lacking the NHP6A and NHP6B proteins. Upper panel: northern blot analysis of a Δnhp6A Δnhp6B mutant strain (RJY6012; Δ) and an isogenic wild-type strain (SEY6210; wt). Ten micrograms of total RNA isolated from cells grown in the absence (–Ser) or presence (+Ser) of serine were electrophoresed in a 1.5% formaldehyde–agarose gel, blotted and hybridized with ³²P-labeled probes for the CHA1 and URA3 genes. Lower panel: β-galactosidase assay of a reporter plasmid, pTK120, containing a CHA1::lacZ translational fusion. Cells grown in the absence (–Ser) or presence (+Ser) of serine were harvested and β-galactosidase activity determined.