Heller K, Kadner R J
J Bacteriol. 1985 Mar;161(3):904-8. doi: 10.1128/jb.161.3.904-908.1985.
The nucleotide sequence of a 2220-base-pair fragment containing the btuB gene of Escherichia coli was determined. There was a single open reading frame which was translated into a 614-amino-acid polypeptide, the first 20 amino acids of which comprised a typical leader sequence. The putative mature or processed form had a molecular weight (66,400) and a composition in close agreement with that determined for the purified receptor. The distribution of amino acids in the receptor protein was similar to that of other outer membrane proteins, showing a fairly even distribution of charged residues and the absence of extensive hydrophobic stretches. The btuB451 mutation appears to alter the receptor to eliminate its ability to function in vitamin B12 uptake without affecting its ligand binding properties. The sequence of the DNA from this mutant was determined and revealed a leucine-to-proline (C-to-T transition) change in the eighth amino acid of the mature form.
测定了包含大肠杆菌btuB基因的一个2220个碱基对片段的核苷酸序列。有一个单一的开放阅读框，它被翻译成一个614个氨基酸的多肽，其前20个氨基酸构成一个典型的前导序列。推测的成熟或加工形式的分子量（66400）和组成与纯化受体所确定的非常一致。受体蛋白中氨基酸的分布与其他外膜蛋白相似，显示带电残基分布相当均匀且没有广泛的疏水区域。btuB451突变似乎改变了受体，使其在维生素B12摄取中丧失功能，但不影响其配体结合特性。测定了该突变体的DNA序列，发现成熟形式的第八个氨基酸发生了亮氨酸到脯氨酸（C到T转换）的变化。
