To determine the biological role, if any, of the NH2-terminal region of beta-1,4-galactosyltransferase (GT; EC 2.4.1.90), we constructed deletion mutants and expressed them in COS-7 cells. Each deletion construct was analyzed for enzymatic activity, protein production and mRNA transcription. All of the deletion mutants were transcribed to produce GT mRNA, but the GT protein was not detected in those constructs whose transmembrane (aa 14-42) domain was deleted. The results suggest that the transmembrane region is essential for the stability of the protein and perhaps contain sequences critical for the proper targeting of the molecule. The possible role of the NH2-terminal signal anchor domain in the in vivo regulation of GT is discussed.

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