Xu Z J, Moffett D B, Peters T R, Smith L D, Perry B P, Whitmer J, Stokke S A, Teintze M
Department of Chemistry and Biochemistry, Montana State University, Bozeman 59717, USA.
J Biol Chem. 1995 Oct 20;270(42):24858-63. doi: 10.1074/jbc.270.42.24858.
Bacterio-opsin is made as a precursor in Halobacterium halobium, which has 13 additional residues at the amino terminus. The codons for these residues have been proposed to form a hairpin structure in the mRNA and play a role in ribosome binding; the leader peptide sequence also has been proposed to have a role in membrane insertion of bacteriorhodopsin (BR). We have made mutations in the bop gene region coding for the leader sequence and expressed the mutant genes in an H. halobium mutant lacking wild-type BR. The leader sequence coding region was found to be important for the stability of the mRNA and for its efficient translation. Single base substitutions in this region that did not affect the amino acid sequence caused significant reductions in protein expression. Deletion of the leader region resulted in unstable mRNA and almost no BR production. Introduction of a new ribosome-binding sequence within the coding region of the mature protein restored mRNA stability and some protein expression. Protein made without the leader peptide was properly assembled in the membrane.
细菌视紫红质在嗜盐菌中以前体形式合成，其氨基末端有另外13个残基。有人提出这些残基的密码子在mRNA中形成发夹结构，并在核糖体结合中起作用；也有人提出前导肽序列在细菌视紫红质（BR）的膜插入中起作用。我们对编码前导序列的bop基因区域进行了突变，并在缺乏野生型BR的嗜盐菌突变体中表达了突变基因。发现前导序列编码区域对mRNA的稳定性及其有效翻译很重要。该区域中不影响氨基酸序列的单碱基替换导致蛋白质表达显著降低。前导区域的缺失导致mRNA不稳定，几乎不产生BR。在成熟蛋白编码区域内引入新的核糖体结合序列可恢复mRNA稳定性和一些蛋白质表达。没有前导肽产生的蛋白质在膜中正确组装。
