Fig. 5.

Arrangement of the Plp1 gene and sequence of alternatively spliced exons derived from what is classically defined as Plp1 intron 1. A: Arrangement of the Plp1 gene is shown at the top. Exons are illustrated by numbered boxes, which are not drawn to scale. Exons 1.1 and 1.2 (gray boxes) are not present in transcripts that encode classic gene products, PLP and DM20. [PLP is encoded by transcripts that select the distal (relative to the tsp) 5− splice site in exon 3 (mRNA contains exon 3A and 3B) and DM20 by transcripts that opt for the proximal (internal) 5− splice site (mRNA is missing exon 3B).] The start site of translation for the classic products is located near the end of exon 1 (bent arrow). RT-PCR analysis was performed with total RNA isolated from TM3 cells and the indicated primers. RT-PCR products were confirmed by DNA sequencing except for products obtained using the exon 1.2/exon 7 primer pair. RT-PCR products obtained with exon1/exon 2 and exon1/exon 1.2 primer pairs were subcloned prior to sequencing. Note that only the classic Dm20 product could be identified by direct sequencing of gel-purified RT-PCR products obtained with the exon 1/exon 4 primer pair due to a mixture of products in larger sized bands. B: Sequence for exon 1.1 (Bongarzone et al., 1999) and exon 1.2 is shown in capital letters and corresponds to Plp1 intron 1 positions 122–230 and 7,224–7,345, respectively (GenBank accession number AF003838). Lower case letters indicate surrounding intronic sequence that is 100% conserved in all splice sites. Internal ATG triplets (prospective initiation codons) are underlined in bold letters, which must be used for productive translation of transcripts that contain exon 1.1 or exon 1.2.