FIG. 8.

Homeostatic responses to S limitation (A) and generation of 1C units from serine and glycine (46) (B). (A) Pathways responding to S limitation are indicated schematically along with the regulators controlling them (ovals). Details of several of the pathways and ligands for the regulators are discussed in the text (also see Table 1). (B) 3-Phosphoglycerate (3PGA) is the central metabolite. The 1C units are transferred to tetrahydrofolate, yielding N⁵,N¹⁰-tetrahydrofolate. The gene products that catalyze the reactions are indicated above the arrows.