Isolation, sequence analysis, and intron-exon arrangement of the gene encoding bovine rhodopsin

We have isolated cDNA clones generated from the mRNA encoding the opsin apoprotein of bovine rhodopsin and used these cDNAs to isolate genomic DNA clones containing the complete opsin gene. Nucleotide sequence analysis of the cloned DNAs has yielded a complete amino acid sequence for bovine rhodopsin and provided an intron-exon map of its gene. The mRNA homologous sequences in the 6.4 kb gene consist of a 96 bp 5' untranslated region, a 1044 bp coding region, and a surprisingly long approximately 1400 bp 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.     

Human dihydrofolate reductase gene organization. Extensive conservation of the G + C-rich 5' non-coding sequence and strong intron size divergence from homologous mammalian genes

The complete human dihydrofolate reductase (DHFR) gene has been cloned from four recombinant lambda libraries constructed with the DNA from a methotrexate-resistant human cell line with amplified DHFR genes. The detailed organization of the gene has been determined by restriction mapping of the cloned fragments and DNA sequencing of all the protein coding regions and adjacent intron segments, and shown to correspond to that of the native human DHFR gene. The gene spans a length of approximately 29 X 10(3) bases from the ATG initiator codon to the end of the 3' untranslated region, and contains five introns that interrupt the protein coding sequence. The number and positions of introns are identical to those found in the mouse gene. By contrast, the size of the homologous introns (with the exception of the first one) varies greatly, up to several fold, in the genes from man, mouse and Chinese hamster; the intron sequences also exhibit a great divergence, except in the junction regions. A striking sequence homology, extending over several hundred nucleotides, exists between the human and mouse gene 5' non-coding regions. These regions are characterized by an unusually high G + C content, 72% and 66% in the human and mouse genes, respectively, which is maintained in the first coding segment and first intron, and is in sharp contrast to the relatively low G + C content (approximately 40%) of the remainder of the gene.     

Nucleotide sequence of a protamine component CII gene of Salmo gairdnerii.

We have isolated, using nick-translated cloned protamine cDNA's as probes, several genomic clones containing protamine gene sequences from a Charon 4A library of Eco R1 digested rainbow trout (Salmo gairdnerii) DNA. One clone was chosen for detailed study and the 2.5 kbp Bam HI-Eco R1 restriction fragment containing the gene was subcloned in the plasmid pBR322. A 920 bp Bg1 II - Bam HI restriction fragment contains a sequence coding for protamine component CII as well as regions 5' and 3' to the mRNA coding portion. Present in the region 5' to the mRNA coding sequence are the promoter associated signals "TATA" box and "CAAT" box. The 5' untranslated region of the mRNA whose length and sequence were not established from the cDNA clones (1) was determined by nuclease mapping and starts within a sequence similar to the "capping signal" found in other genes. The protamine gene for CII contains no introns, a situation common to most histone genes, but, unlike the histone genes does not occur close to other protamine genes in a "cluster".