STRUCTURE AND REGULATION OF CATFISH AND RAT SOMATOSTATINS (MOLECULAR BIOLOGY, DNA SEQUENCE, HORMONES)
Abstract
The nucleotide sequence of the two somatostatins from channel catfish (Icthalurus punctatus) was determined after identification of hybridizing sequences with an oligonucleotide probe directed against the C-terminal portion of somatostatin-14. Nucleotide sequence analysis shows that the mRNA for somatostatin-14 from catfish codes for the biologically active peptide found in all vertebrate species, while somatostatin-22 is a unique form of the peptide contained in a different mRNA. Techniques used in the catfish system were used to isolate the mRNA for somatostatin-14 from a medullary thyroid carcinoma of rat, a tissue abundant in somatostatin. The rat somatostatin mRNA sequences were subsequently used as a hybrdization probe to isolate the structural gene for rate somatostatin from a phage gene bank. Sequence analysis of the rat somatostatin gene was accomplished by a combination of chemical and enzymatic means. The gene encodes two small exons of 238 and 367 base pairs, separated by one small intron. The 5' promoter elements responsible for somatostatin gene expression have been examined by a transient expression assay. A chimeric gene containing 750 base pairs of the 5' region of the somatostatin gene fused to coding sequences for chloramphenicol acetyltransferase (CAT) was used to transfect a somatostatin-producing cell line and a control cell line. The somatostatin promoter was found to be functional only in the somatostatin-synthesizing cell line. This result has ramifications as to the cell-specific control of expression of this gene. Additional characterization of the flanking regions of the gene was carried out by Southern hybridizations and nuclease analysis of potential Z-DNA forming sequences.
Degree
Ph.D.
Subject Area
Biochemistry
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