B. A fragment of β-galactosidase.
When somatostatin is produced by recombinant DNA technology in E. coli, it is initially attached to a fragment of β-galactosidase.
In recombinant DNA technology, the gene encoding somatostatin is inserted into a plasmid vector, which is then introduced into E. coli cells for expression. To facilitate the identification and purification of the expressed somatostatin, a common approach is to fuse it with a reporter protein, such as a fragment of β-galactosidase.
The fusion protein consists of the somatostatin peptide sequence linked to a portion of β-galactosidase. This allows the detection and isolation of cells that are producing the desired somatostatin peptide by using colorimetric or other assays that detect the activity or presence of β-galactosidase.
By fusing somatostatin to a fragment of β-galactosidase, the expressed somatostatin can be easily identified and separated from other cellular components during the purification process.
Therefore, the correct answer is B. A fragment of β-galactosidase.