Mediates positive regulation of the ptsG/glcA and glcB genes by functioning as an antiterminator factor of transcription via its interaction with the RNA-antiterminator (RAT) sequence located upstream of the ptsG/glcA gene. Homodimer. Phosphorylated by HPr, which enhances dimer formation and leads to activation. With phosphorylation at His-105. Belongs to the transcriptional antiterminator BglG family. GlcT subfamily.