Difference in sizes of human compared to murine alpha-subunits of the glycoprotein hormones arises by four-codon gene deletion or insertion.

The research article examines the difference in size between human and animal alpha-subunits of glycoprotein hormones, attributing it to a deletion or insertion of four codons during gene expression instead of post-translational proteolysis.

Objective of the Research

• The research aims to determine the cause of the size difference between human and animal (specifically murine, equine, bovine, and ovine) alpha subunits of glycoprotein hormones, which is about four amino acids.

Methods Used

• The researchers used recombinant DNA techniques to figure out the nucleotide sequences of the mRNAs producing the precursors of the alpha subunits in mouse Thyroid Stimulating Hormone (TSH) and rat gonadotropins.
• They then compared the sequences, as well as their translated amino acid sequences, with those of the precursor alpha-subunits of hCG and the gene encoding the human alpha-subunit.

Research Findings

• The research indicated that the size difference of four amino acids between the apoproteins of the murine and human alpha-subunits resulted from either a deletion or an insertion of four codons near the location of the second intron in the human gene.
• Also, it became apparent that the sequence of the four absent codons in the mRNA encoding the precursor hCG alpha-subunit resembles a part of the sequence found in the 3′ end of the intron.

Conclusion

• Based on these findings, the researchers concluded that the size difference between the human and animal alpha-subunits isn’t caused by post-translational proteolysis; it originates at the gene level. This essentially means that the difference is fundamentally genetic rather than biochemical.