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1400 by 3′ untranslated region, and are divided into five exons by four introns that interrupt the coding region. Secondary structure analysis predicts that the bovine rhodopsin chain, like that of bacteriorhodopsin, contains seven transmembrane segments. Interestingly, three of the four introns are immediately distal to the codons for three of these segments, and one of these introns marks the boundary between the C-terminal domain and a transmembrane domain.
doi:10.1016/0092-8674(80)90617-0 
Copyright © 1980
Article
Two mRNAs can be produced from a single immunoglobulin μ gene by alternative RNA processing pathways
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P. Earlya, J. Rogersb, M. Davisa, K. Calamea, M. Bonda, R. Wallb and L. Hooda
Received 17 March 1980.
Abstract
As shown in the accompanying paper, μ chains of the membrane-bound (μm) and secreted (μs) forms of IgM are encoded by two species of mRNA. Cloned cDNAs produced from the two μ mRNAs of M104E mouse myeloma tumors differ only at their 3′ ends, which encode either the μm or μs C terminus. In this paper, we show that both μm and μs mRNAs are produced from transcripts of a single μ gene. The last 187 nucleotides of μs mRNA are derived from DNA contiguous with the 3′ end of the sequence encoding the Cμ4 domain. The μm cDNA clone does not include these 187 nucleotides, but instead contains 392 nucleotides derived from two exons located 1850 bp 3′ to the Cμ4 sequence. Comparison of genomic and cDNA sequences show that in μm mRNA, an RNA splice of 1850 nucleotides joins a site in the coding sequence at the end of Cμ4 with a site at the beginning of the first membrane-specific exon. A second RNA splice of 118 nucleotides joins sequences transcribed from the first and second membrane-specific exons. The differences observed between μm and μs cDNAs suggest that developmental control of the site at which poly(A) is added to transcripts of the μ gene determines the relative levels of μm or μs chain synthesis. We discuss possible models for the control of μ gene transcripts and the significance of this form of developmentally regulated RNA processing for the evolution of eucaryotic “split genes.”
