Mechanism of production of multiple mRNAs for the major sialoglycoprotein of human erythrocytes, glycophorin A

Hamid, Jawed (1991) Mechanism of production of multiple mRNAs for the major sialoglycoprotein of human erythrocytes, glycophorin A. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Glycophorins are a family of human erythrocyte membrane glycoproteins. At least four different sialoglycoproteins glycophorins, A (or α), B (or δ), C (or β) and D (or γ) have been detected in humans. Glycophorin A is the major sialic acid-containing protein of human erythrocyte membranes. It consists of 131 amino acids distributed in three structural domains. Glycophorin A is encoded by a single gene which gives rise to three different mRNAs, large (2.8 kb ), medium (1.7 kb) and small (1.0 kb) in reticulocytes and in K562, a human erythroleukaemia cell line expressing glycophorin A on its surface. -- Six clones were isolated from a cDNA library constructed with K562 cell mRNA in λgt10 phage using as a probe a synthetic oligonucleotide (GPA-N2) encoding amino acid numbers 30 to 40 of glycophorin A. Nucleotide sequencing of the six clones revealed that all contain an identical protein coding region except for the well known glycophorin AM-AN polymorphism and essentially identical 5" untranslated regions. In contrast, clones differ substantially in the length of their 3" untranslated regions. Examination of the 3 ’ untranslated region of the largest clone revealed seven poly(A) addition signals (AATAAA). To study how the single gene encoding glycophorin A generates three different mRNAs, primer extension analysis and Northern blotting experiments were performed. These experiments supported the findings of the cDNA sequencing and revealed that the three glycophorin A mRNAs differ in the length of their 3 ' untranslated region. The primary structure of the three glycophorin A mRNAs is deduced based upon the nucleotide sequence of various cDNAs, primer extension analysis and Northern blotting experiments. A mechanism is proposed for the generation of the three glycophorin A mRNAs from a single glycophorin A gene that involves differential processing of the 3 ' end of glycophorin A pre-mRNA utilizing multiple poly(A) addition signals.

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