Genomic clones of the chloroplastic glutamine synthetase...

Genomic clones of the chloroplastic glutamine synthetase gene $(g \ln 2)$ of maize are cleaved into two fragments by digestion with restriction endonuclease HindIII, whereas full-length maize $g / m 2$ cDNA clones are not cut by HindIII. Explain these results.

Key Concepts

Genomic DNA

Genomic DNA refers to the complete set of DNA in an organism, including both coding regions (exons) and non-coding regions (introns, regulatory sequences, and other intergenic sequences). In genomic clones, the presence of introns means that they retain sequences that are not present in mature mRNA, which can include recognition sites for restriction enzymes.

cDNA

cDNA, or complementary DNA, is synthesized from mature mRNA through the process of reverse transcription. Because mature mRNA has been processed to remove introns, cDNA represents only the gene's coding sequence (exons). As a result, cDNA may lack specific restriction sites that are located in intronic regions of the genomic DNA.

Introns and Exons

Introns are non-coding regions of a gene that are present in the genomic DNA and removed during RNA splicing, while exons are coding sequences that remain in the mature mRNA and cDNA. Their distinct compositions are crucial in understanding differences observed in restriction enzyme digestion patterns between genomic clones and cDNA clones.

Restriction Endonucleases

Restriction endonucleases are enzymes that cut DNA at specific nucleotide sequences. The differential digestion patterns observed in the experiment can be attributed to the presence of a HindIII recognition site within an intron in the genomic DNA that is absent in the cDNA, which contains only exonic sequences.

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