The genes encoding geranylgeranyl transferase α-subunit and transglutaminase 1 are very closely linked but not functionally related in terminally differentiating keratinocytes

We report here the entire exon/intron structure of the gene encoding the α-subunit of human Rab geranylgeranyl transferase (RABGGTA) gene, which is positioned in a tandem head-to-tail arrangement with the transglutaminase 1 (TGM1) gene, and its polyadenylation signal sequence is located just 2.3 kbp upstream of the capsite of TGM1. Even though TGM1 and RABGGTA have different functions, their close localization raised the question as to whether they are functionally related in the epidermis. To address this question, we have studied the expression of the two genes by RT-PCR in normal human epidermal keratinocytes cultured under various differentiation conditions. While the expression of the TGM1 gene is markedly affected by the calcium concentration of the medium, all trans retinoic acid, vitamin D₃, and TPA treatment, the expression of the RAB-GGTA gene was unaffected by these reagents. Taken together, even though these two genes are unusually closely linked, they are not functionally related in the terminal differentiation program of epidermal keratinocytes.