Structure of the gene for human butyrylcholinesterase. Evidence for a single copy

We have isolated five genomic clones for human butyrylcholinesterase (BChE), using cDNA probes encoding the catalytic subunit of the hydrophilic tetramer [McTiernan et al. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 6682-6686]. The BChE gene is at least 73 kb long and contains four exons. Exon 1 contains untranslated sequences and two potential translation initiation sites at codons -69 and -47. Exon 2 (1525 bp) contains 83% of the coding sequence for the mature protein, including the N-terminal and the active-site serine, and a third possible translation initiation site (likely functional), at codon -28. Exon 3 is 167 nucleotides long. Exon 4 (604 bp) codes for the C-terminus of the protein and the 3' untranslated region where two polyadenylation signals were identified. Intron 1 is 6.5 kb long, and the minimal sizes of introns 2 and 3 are estimated to be 32 kb each. Southern blot analysis of total human genomic DNA is in complete agreement with the gene structure established by restriction endonuclease mapping of the genomic clones: this strongly suggests that the BChE gene is present in a single copy.     

Structure and sequence of the human alpha-L-iduronidase gene.

In humans, a deficiency of the lysosomal hydrolase alpha-L-iduronidase (IDUA;EC 3.2.1.76) results in the lysosomal storage of the glycosaminoglycans heparan sulfate and dermatan sulfate, thereby causing the lysosomal storage disorder mucopolysaccharidosis type I. The gene for IDUA is split into 14 exons spanning approximately 19 kb. We report the sequence of two non-contiguous segments of the IDUA gene, one 1.8-kb segment containing exons 1 and 2 and surrounding sequences and a second segment of 4.5 kb containing the last 12 exons. The potential promoter for IDUA has only GC box type consensus sequences consistent with a housekeeping promoter and is bounded by an Alu repeat sequence. The first two exons of IDUA are separated by an intron of 566 bp, then there is a large intron of approximately 13 kb, and the last 12 exons are clustered within 4.5 kb. No consensus polyadenylation signal was found in the 3' untranslated region, although two variant polyadenylation signals are proposed.     

Multiple polyadenylation sites in a Drosophila tropomyosin gene are used to generate functional mRNAs.

The gene encoding muscle tropomyosin I in Drosophila is alternatively spliced in embryonic and thoracic muscle to generate two sizes classes of RNAs. By Northern blot analysis, the embryonic RNA class shows a broad RNA band of hybridization of 1.3 kb and a more sharply defined, less abundant RNA band at 1.6 kb. The thoracic class of RNAs, on the other hand, consists of a broad hybridization band at 1.7 kb and a more sharply defined band at 1.9 kb. Each size class of RNA encodes a different tropomyosin isoform. The two classes of alternatively spliced RNAs utilize the same 3' terminal exon of the gene. The DNA sequence of this exon reveals a cluster of several polyadenylation signals (AAUAAA) or polyadenylation-like signals. We show here by S1 nuclease protection analysis that at least five and possibly seven of these polyadenylation or polyadenylation-like sequences are associated with in vivo embryonic and thoracic mRNA cleavage processing sites. Six of these S1 sites are clustered within 119 bp and a seventh is located 255 bp downstream. At least one of the polyadenylation-like signal sequences appears to be an unusual AACAAA sequence. In addition we also show that these mRNAs function in vitro to synthesize muscle tropomyosins.