Intronless human dihydrofolate reductase genes are derived from processed RNA molecules

Area of Science:

• Molecular Biology
• Genetics
• Bioinformatics

Background:

• Dihydrofolate reductase (DHFR) is a crucial enzyme in nucleotide synthesis and DNA repair.
• Understanding the structure and origin of DHFR genes is important for comprehending gene regulation and evolution.
• Recombinant bacteriophages are valuable tools for cloning and studying human DNA sequences.

Purpose of the Study:

• To isolate and characterize recombinant bacteriophages containing human dihydrofolate reductase (DHFR) coding sequences.
• To investigate the structural features and potential origins of novel DHFR gene variants.
• To identify genetic elements associated with processed pseudogenes.

Main Methods:

• Screening of human DNA clone libraries using recombinant bacteriophages.
• Sequence analysis of isolated recombinant clones to identify DHFR coding sequences and structural elements.
• Homology comparisons between novel sequences and the normal human DHFR gene.

Main Results:

• Isolation of three recombinant bacteriophage groups containing human DHFR coding sequences.
• Identification of two intronless DHFR genes (hDHFR-psi 1 and hDHFR-psi 2) with a 3' A-rich tract, suggesting derivation from processed RNA.
• hDHFR-psi 1 exhibits high homology to the normal DHFR gene, while hDHFR-psi 2 contains termination codons and lower homology.
• Direct repeat sequences flanking the 3' end of hDHFR-psi 2 suggest its origin as an inserted DNA sequence.

Conclusions:

• The intronless DHFR genes hDHFR-psi 1 and hDHFR-psi 2 likely originated from processed messenger RNA (mRNA) molecules.
• The presence of terminal direct repeats in hDHFR-psi 2 indicates its potential origin from transposable elements or retroviral integration.
• These findings contribute to the understanding of gene duplication, pseudogene formation, and DNA sequence evolution in the human genome.