Contain the same coding sequences have been identified in liver and kidney. These two mRNA variants are likely to be generated from alternate transcription from two promoters [13]. In contrast to our study, Wang et al [19] compared the 59-UTR sequences of three human PC mRNA variants namely, variant 1 (NM_000920.3), 2 (NM_022172.2) and 3 (BC011617.2) deposited at the NCBI database to the genomic sequence of human PC gene and concluded that these variants are alternatively spliced from four 59-UTR exons, i.e. UE1, UE2, UE3 and UE4, respectively, with the distal, middle and proximal promoters JI 101 site located immediately upstream of exons UE1, UE2 and UE4, respectively [19]. However, we re-examined the alignment of those three variants and found that variants 1 and 3 share the common 83 nucleotides upstream of the first initiation codon, while variant 1 contains 11 additional nucleotides at its 59-end (see Figure 1A). Wang et al [19] reported that this extra sequence is derived from an upstream exon, UE1. However, direct comparison of 59-UTR sequences of variants 1 and 3 with the genomic sequence of the human PC gene clearly showed that these extra 11 nucleotides in variant 1 are located immediately upstream of UE2, thus forming part of this exon. Therefore, it is highly likely that the 11 nucleotide Sapropterin (dihydrochloride) site segment in variant 1 could easily be a truncated transcript or result from the use of multiple start sites of the TATA-less genes. In agreement with Wang et al [19], the 59-UTR sequence of variant 2 is derived from a separate 59 UTR exon which is located proximal to the first coding exon. The lack of an intron between UE1 and UE2 rules out the possibility that there is a middle promoter located between these two upstream exons as proposed by Wang et al [19]. Based on this new information we revised the structural organization of the human PC gene as follows: the human PC gene contains only three 59-UTR exons, i.e. UE1/UE2, UE3 and UE4, with the proximal promoter located upstream of UE4 and the distal promoter located upstream of UE1/UE2. Transcription initiated from the proximal promoter produces variant 2 while transcription from the distal promoter produces variants 1 and 3 (Figure 1B). The presence of two alternative promoters of human PC gene appears to recapitulate that of the rat [14] and mouse PC genes [14]. This is in contrast to bovine PC gene which possesses three promoters, the proximal (P1), middle (P2) and distal (P3) promoter [20]. However, there is no report about which of these promoters is highly active in bovine pancreatic b-cells. Although the two PC mRNA isoforms have 1662274 been described in liver and kidney [13,19], it is not known which of these isoform(s) is expressed in human pancreatic islets. To address this question, we performed an RT-PCR analysis of cDNA prepared from human islets using two forward primers that specifically bind to the 59-UTRs of variant 1 and variant 2 together with a reverse primerthat binds to exon 1 (see Figure 1B). With these primers, the amplicons with sizes of 173 bp and 200 bp, representing variant 1 and variant 2 were expected. As shown in Fig. 1C, both primer sets were able to amplify the 173 bp and 200 bp PCR products representing variants 1 and 2 which are produced from both proximal and distal promoters of the human PC gene from HepG2 cDNA (lanes 4 and 5), respectively. This result indicated that both proximal and distal promoters are active in liver. In a sharp contrast, RT-PCR of cDNA prepared fro.Contain the same coding sequences have been identified in liver and kidney. These two mRNA variants are likely to be generated from alternate transcription from two promoters [13]. In contrast to our study, Wang et al [19] compared the 59-UTR sequences of three human PC mRNA variants namely, variant 1 (NM_000920.3), 2 (NM_022172.2) and 3 (BC011617.2) deposited at the NCBI database to the genomic sequence of human PC gene and concluded that these variants are alternatively spliced from four 59-UTR exons, i.e. UE1, UE2, UE3 and UE4, respectively, with the distal, middle and proximal promoters located immediately upstream of exons UE1, UE2 and UE4, respectively [19]. However, we re-examined the alignment of those three variants and found that variants 1 and 3 share the common 83 nucleotides upstream of the first initiation codon, while variant 1 contains 11 additional nucleotides at its 59-end (see Figure 1A). Wang et al [19] reported that this extra sequence is derived from an upstream exon, UE1. However, direct comparison of 59-UTR sequences of variants 1 and 3 with the genomic sequence of the human PC gene clearly showed that these extra 11 nucleotides in variant 1 are located immediately upstream of UE2, thus forming part of this exon. Therefore, it is highly likely that the 11 nucleotide segment in variant 1 could easily be a truncated transcript or result from the use of multiple start sites of the TATA-less genes. In agreement with Wang et al [19], the 59-UTR sequence of variant 2 is derived from a separate 59 UTR exon which is located proximal to the first coding exon. The lack of an intron between UE1 and UE2 rules out the possibility that there is a middle promoter located between these two upstream exons as proposed by Wang et al [19]. Based on this new information we revised the structural organization of the human PC gene as follows: the human PC gene contains only three 59-UTR exons, i.e. UE1/UE2, UE3 and UE4, with the proximal promoter located upstream of UE4 and the distal promoter located upstream of UE1/UE2. Transcription initiated from the proximal promoter produces variant 2 while transcription from the distal promoter produces variants 1 and 3 (Figure 1B). The presence of two alternative promoters of human PC gene appears to recapitulate that of the rat [14] and mouse PC genes [14]. This is in contrast to bovine PC gene which possesses three promoters, the proximal (P1), middle (P2) and distal (P3) promoter [20]. However, there is no report about which of these promoters is highly active in bovine pancreatic b-cells. Although the two PC mRNA isoforms have 1662274 been described in liver and kidney [13,19], it is not known which of these isoform(s) is expressed in human pancreatic islets. To address this question, we performed an RT-PCR analysis of cDNA prepared from human islets using two forward primers that specifically bind to the 59-UTRs of variant 1 and variant 2 together with a reverse primerthat binds to exon 1 (see Figure 1B). With these primers, the amplicons with sizes of 173 bp and 200 bp, representing variant 1 and variant 2 were expected. As shown in Fig. 1C, both primer sets were able to amplify the 173 bp and 200 bp PCR products representing variants 1 and 2 which are produced from both proximal and distal promoters of the human PC gene from HepG2 cDNA (lanes 4 and 5), respectively. This result indicated that both proximal and distal promoters are active in liver. In a sharp contrast, RT-PCR of cDNA prepared fro.
