Activates the transcription of the gabTD operon. Is also a repressor of its own expression, both in the presence and absence of GABA. Binds specifically to the DNA region overlapping the -35 region of the gabT promoter and the -10 and +1 regions of the gabR promoter. Principally regulates the utilization of gamma-aminobutyrate. In the C-terminal section; belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.