Insertion Signal and Membrane Anchor Functions of the Amino Terminus of Cytochrome P45011C2
Browne, Nancy F.
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Permalink
https://hdl.handle.net/2142/71456
Description
Title
Insertion Signal and Membrane Anchor Functions of the Amino Terminus of Cytochrome P45011C2
Author(s)
Browne, Nancy F.
Issue Date
1988
Department of Study
Physiology and Biophysics
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Abstract
Proteins destined for export from a cell are synthesized in a larger precursor form with the cleaved pre sequence acting as the signal for translocation across the endoplasmic reticulum. Proteins integrated into the endoplasmic reticulum also possess translocation signals, but such signals are not easily recognized if the signal is not cleaved. The amino terminus of cytochrome P45011C2 was examined for properties of signal sequences. A fusion between the amino terminus of P45011C2 and stretched preproparathyroid hormone was formed by ligation of DNA coding sequences in an SP6 promoter plasmid. The translation of the hybrid protein was arrested by SRP but the protein was not translocated to the interior of microsomal membrane vesicles. Full length P450 proteins integrated into microsomal membranes in an SRP dependent manner, while partial proteins lacking the amino terminus failed to integrate. P450 transcripts produced more than one translation product in cell-free systems from initiation at internal methionine codons. P45011C2 has been shown to be the same protein as P450 K from rabbit kidney. This paper presents evidence that the amino terminus of P45011C2 is an insertion anchor rather than a translocation signal, and is probably the only topogenic domain of the protein. A model is presented to differentiate between insertion and translocation competent anchor sequences.
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