The structure of rat preproinsulin genes

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Rats possess two nonallelic insulin genes, designated I and II.
• Understanding the structural organization of these genes is crucial for insights into insulin biosynthesis and evolution.

Purpose of the Study:

• To elucidate the detailed structure of rat insulin genes I and II.
• To identify potential regulatory elements or novel precursors involved in insulin biosynthesis.

Main Methods:

• Cloning and sequencing of double-stranded cDNA copies of preproinsulin mRNA I and II.
• Southern blotting technique to create a restriction map of the chromosomal genes.
• Isolation of both insulin genes from a rat DNA library in phage lambda.
• Restriction endonuclease analysis and direct DNA sequencing.
• Identification of nuclear RNA molecules using transcribed intronic sequences as probes.

Main Results:

• Rat insulin gene II contains two introns: a 490 bp intron and a 119 bp intron located upstream of the initiation codon.
• Rat insulin gene I is not interrupted within its protein-coding region but contains an intron homologous to the 119 bp intron of gene II.
• Nuclear RNA molecules larger than preproinsulin mRNA, containing transcribed intronic sequences, were identified, suggesting a new precursor stage.

Conclusions:

• The duplicated rat insulin genes exhibit distinct intron-exon structures, with gene II being more complex.
• The identified larger nuclear RNA molecules represent a novel precursor in insulin biosynthesis, containing intronic sequences.
• Comparative analysis of insulin genes across species is underway to understand the evolutionary history of the 490 bp intron.