Klösgen R B, Saedler H, Weil J H
Max-Planck-Institut für Züchtungsforschung, Egelspfad, Köln, Federal Republic of Germany.
Mol Gen Genet. 1989 May;217(1):155-61. doi: 10.1007/BF00330955.
The transit peptide of the waxy protein of maize which in the maize plant targets this protein only into amyloplasts was used for in vitro protein transport experiments with isolated amyloplasts from maize and chloroplasts from maize, pea and potato. In the presence of both intact and disrupted amyloplasts an artificial preprotein (TP30), consisting of the waxy transit peptide plus the first 34 amino acids of the mature waxy protein fused in-frame to the beta-glucuronidase of Escherichia coli, is processed to the size expected when the transit peptide is cleaved off. The chloroplasts studied show in vitro import and correct processing of both TP30 and the authentic waxy protein, but not of the beta-glucuronidase without the waxy transit peptide. The in vitro import of TP30 into chloroplasts is almost as efficient as that of the precursor of the small subunit of pea ribulose-1,5-bisphosphate carboxylase, a nuclear-encoded chloroplast protein, whereas the waxy protein accumulates to a lesser extent in the chloroplasts. Since the amino-terminal transit peptides of TP30 and the waxy precursor are the same, this difference must be due to the mature part of the waxy protein. One possible explanation is the observed instability of the waxy protein in the presence of chloroplasts.
玉米蜡质蛋白的转运肽在玉米植株中仅将该蛋白靶向导入造粉体，利用它对来自玉米的分离造粉体以及来自玉米、豌豆和马铃薯的叶绿体进行体外蛋白转运实验。在完整和破碎的造粉体存在的情况下，一种人工前体蛋白（TP30），由蜡质转运肽加上成熟蜡质蛋白的前34个氨基酸与大肠杆菌β-葡萄糖醛酸酶框内融合而成，在转运肽被切割后会被加工成预期大小。所研究的叶绿体显示出对TP30和天然蜡质蛋白的体外导入和正确加工，但对没有蜡质转运肽的β-葡萄糖醛酸酶则不然。TP30导入叶绿体的效率几乎与豌豆核酮糖-1,5-二磷酸羧化酶小亚基前体（一种核编码的叶绿体蛋白）相同，而蜡质蛋白在叶绿体中的积累程度较低。由于TP30和蜡质前体的氨基末端转运肽相同，这种差异必定是由于蜡质蛋白的成熟部分。一种可能的解释是观察到蜡质蛋白在叶绿体存在时不稳定。
