Cloning and sequence analysis of a cDNA encoding rat preprocholecystokinin

Area of Science:

• Molecular Biology
• Endocrinology
• Genetics

Background:

• Medullary thyroid carcinoma in rats exhibits high levels of immunoreactive cholecystokinin (CCK).
• Understanding the genetic basis of CCK production in tumors is crucial for cancer research.

Purpose of the Study:

• To isolate and characterize the complementary DNA (cDNA) encoding the precursor to cholecystokinin (CCK) in a rat medullary thyroid carcinoma.
• To analyze the structure of the rat preprocholecystokinin gene, including non-coding regions and potential regulatory elements.

Main Methods:

• Poly(A) RNA isolation from rat medullary thyroid carcinoma.
• Synthesis of double-stranded cDNA and insertion into pBR322 plasmid.
• Bacterial colony screening using a hybridization probe derived from porcine CCK-8 amino acid sequence.
• Nucleotide sequencing of the identified CCK cDNA.

Main Results:

• The nucleotide sequence of rat preprocholecystokinin cDNA was determined.
• The cDNA comprises 33 nucleotides (5'-noncoding), 345 nucleotides (coding for a 115-amino acid precursor), and 199 nucleotides (3'-noncoding).
• A putative transcriptional control sequence (TATA-like) and start site were identified upstream of the coding region. CCK mRNA is approximately 750 nucleotides long and similar in size across different rat tissues.

Conclusions:

• The study successfully cloned and sequenced the cDNA for rat preprocholecystokinin, providing insights into its precursor structure.
• Identification of potential transcriptional regulatory elements suggests mechanisms for CCK gene expression control.
• The findings contribute to understanding CCK gene expression in both normal tissues and thyroid carcinoma.