Identification and characterization of two novel and differentially expressed isoforms of human a2-and a1-globin genes
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In most references, the transcription initiation site for the a2-and a1-globin genes has been described to lie 37 bp upstream of the translation initiation codon, however, a review of data repositories such as GenBank and Ensembl showed a report of the a2-globin transcription initiation site occurring at position 66 relative to the initiation codon. To confirm the occurrence of these isoforms for both the a2-and a1-globin genes and to document their expression levels, we initiated our current investigation. Total RNA from the peripheral blood of 15 healthy volunteers was analyzed using both semi-quantitative-polymerase chain reaction (PCR) and real-time (ReTi-PCR) protocols developed in our laboratory, with primers designed to enable distinction between the a2-and a1-globin transcripts.We observed two distinct PCR products for each of the globin genes. Subsequent DNA sequencing of 11 individual PCR products revealed that the a2-and a1-globin transcripts are present in both a long and a short isoform, initiating at positions 66 and 37, respectively. The shorter (37) isoform is expressed approximately 10,000100,000 times more strongly than the longer isoform, demonstrating differential expression within the healthy population. This study, for the first time, confirms the presence of two isoforms for both the a2-and a1-globin genes with varying transcription levels in healthy individuals. The short isoform is expressed at significantly higher levels than the longer isoform for both a2 and a1 genes. Therefore, based on our observations, we propose that despite the contribution of the long isoforms to the total a-globin RNA pool, the short isoforms are the main physiological transcripts. © 2012 Informa Healthcare USA, Inc.
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