The human glucose transporter can insert posttranslationally into microsomes.
RNA transcripts encoding the complete human glucose transporter ( GT) or fragments of GT corresponding to the NH2-terminal 340 amino acids (GT-N) or the COOH-terminal 148 amino acids (GT-C) were synthesized in vitro from SP6 plasmids. The corresponding polypeptides were synthesized in reticulocyte or wheat germ cell-free systems and their insertion into pancreatic microsomes was assessed by endoglycosidase H and trypsin digestion or alkaline extraction of membranes. The following observations were made: both GT and GT-N can insert posttranslationally into microsomes; GT contains at least two distinct signal sequences; both co- and posttranslational insertion of GT-N are mediated by a signal recognition particle (SRP)-SRP receptor-dependent mechanism; and SRP is required both for targeting the polypeptide to the membrane and for initiating the actual insertion process. We propose a model for the biosynthesis of GT and proteins of similar membrane topology which does not require a tight ribosome-membrane interaction.[1]References
- The human glucose transporter can insert posttranslationally into microsomes. Mueckler, M., Lodish, H.F. Cell (1986) [Pubmed]
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