ISSN:
1617-4623
Keywords:
Membrane receptor
;
NPT II fusion proteins
;
Post-translational processing
;
Ribulose-1,5-bisphosphate carboxylase small subunit
;
Transport efficiency
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Transport of foreign proteins into chloroplasts was studied in a transgenic plant expressing two different fusion proteins, the transit peptide (TP) of ribulose-bisphosphate carboxylase small subunit (SS) fused to neomycin phosphotransferase (TP-NPT II) and, the same transit peptide plus the amino-terminal 23 amino acids of mature SS linked to NPT II. The second fusion protein (TP-SS-NPT II) was found in isolated chloroplasts but accumulated to a lesser degree than the first (TP-NPT II). This finding does not support the hypothesis that the highly conserved amino acid sequence surrounding the cleavage site between the transit peptide (TP) and mature SS is required for efficient transport. This cleavage region shows a markedly higher conservation than either the mature protein or the TP sequences in SS genes from different plant species. Evidence is presented indicating that the transport of the TP-SS-NPT II precursor is diminished as a result of competition between the rate of its uptake and the rate of its degradation by cytosolic proteases. In an attempt to identify further regions in the TP involved in transport and processing, we designed derivatives of both the TP-SS-NPT II and TP-NPT II precursors. A derivative of TP-SS-NPT II lacking the amino acids at the processing site was expressed in plants and was shown to be transported and processed. A derivative of TP-NPT II comprising the first 41 amino acids (out of 57) of the transit peptide linked to NPT II was also expressed in plants. This protein was not imported into the organelles; however a significant amount of partially processed fusion protein was found to be attached to the outer membrane of the chloroplast.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00338082
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