Structure of the Human Type IV CollagenCOL4A6Gene, Which Is Mutated in Alport Syndrome-Associated Leiomyomatosis

Basement membrane (type IV) collagen, a subfamily of the collagen protein family, is encoded by six distinct genes in mammals. Three of those,COL4A3, COL4A4,andCOL4A5,are linked with Alport syndrome (hereditary nephritis). Patients with leimoyomatosis associated with Alport syndrome have been shown to have deletions in the 5′ end of theCOL4A6gene, in addition to having deletions inCOL4A5(Zhouet al., Science261: 1167–1169, 1993). The humanCOL4A6gene is reported to be 425 kb as determined by mapping of overlapping YAC clones by probes for its 5′ and 3′ ends. In the present study we describe the complete exon/intron size pattern of the humanCOL4A6gene. The 12 λ phage clones characterized in the study spanned a total of 110 kb, including 85 kb of the actual gene and 25 kb of flanking sequences. The overlapping clones contained all 46 exons of the gene and all introns, except for intron 2. Since the total size of the exons and all introns except for intron 2 is about 85 kb, intron 2 must be about 340 kb. All exons of the gene were assigned toEcoRI restriction fragments to facilitate analysis of the gene in patients with leiomyomatosis associated with Alport syndrome. The exon size pattern ofCOL4A6is highly homologous with that of the human and mouseCOL4A2genes, with 27 of the 46 exons ofCOL4A6being identical in size between the genes.     

Comparative analysis of the structural organization of two closely related vitellogenin genes in X. laevis

The structural organization of the two closely related vitellogenin genes A1 and A2 has been determined and compared by electron microscopy. In both genes the mRNA-coding sequence of 6 kb is interrupted 33 times, leading to a total gene length of 21 kb for gene A1 and 16 kb for gene A2. Thus both genes have a mean exon length of 0.175 kb, while the mean intron length is 0.45 kb in gene A1 and 0.31 kb in gene A2. Because the introns interrupt the structural sequence at homologous positions in genes A1 and A2, we suggest that these two genes are the products of a duplication of an ancestral gene which had an intron-exon arrangement similar to that of the extant genes. Since the duplication event, the sequence and length of the analogous introns have changed rapidly, whereas homologous exons have diverged to an extent of only 5% of their sequences. The results suggest different mechanisms of evolution for exons and introns. While the exons evolved primarily by point mutations, such mutations, as well as deletion, insertion and duplication events, were important in the evolution of the introns.     

Complete structure of the human transferrin gene. Comparison with analogous chicken gene and human pseudogene

The complete structure of the human transferrin gene is presented. This gene has a total size of about 33.5 kb and is organized in 17 exons separated by 16 introns. The chicken ovotransferrin gene has a size of 10.5 kb and is also organized in 17 exons and 16 introns. The analysis of the structure of the two genes confirm, at the gene level, that transferrins originated by a gene duplication phenomenon. Finally, the existence of a new member of the transferrin family, a human transferrin non-processed pseudogene is demonstrated.     

Human desmin-coding gene: complete nucleotide sequence, characterization and regulation of expression during myogenesis and development

A recombinant clone encoding for the human desmin gene (des) has been isolated and characterized and its complete nucleotide sequence has been determined. The 8.4-kb gene has nine exons separated by introns ranging in size from 0.1-2.2 kb. Comparison of the human des gene with that of the hamster has shown that there is a full correspondence in position, size and sequence of the exons. There are eight introns in both the human and the hamster des genes. Although the nucleotide sequence of the introns reveals a large divergence, splice junction sequence signals are conserved. A particularly striking feature of the human des gene is the 1.2-kb repetitive sequence found in the introns. These sequences all belong to the human AluI family. When the 5'- and 3'-untranslated regions of the human vim and des genes were compared it was found that there was a 16-mer consensus element similar to that described by Quax et al. [Cell 43 (1985) 327-338] for the hamster and an 11-bp sequence with homology to the distal regulatory sequence of human and mouse alpha-cardiac actin-coding genes [Minty and Kedes, Mol. Cell. Biol. 6 (1986) 2125-2136] in the 5'-flanking region. The 3'-untranslated region of the human des gene was found to be conserved when compared to the hamster des gene. Only one species of desmin RNA of 2.2 kb was found in human striated and smooth muscle both in vivo and in vitro.     

Polycalin (chlorophyllid A binding protein): a novel, very large fluorescent lipocalin from the midgut of the domestic silkworm Bombyx mori L

We studied a protein from the midgut of the silkworm Bombyx mori characterized by its ability to bind the prosthetic group of chlorophyll, that confers fluorescent properties to this protein. Several techniques, 2D electrophoresis purification, MS-MS and Maldi-TOF peptide sequencing, RT-PCR and nucleotide sequencing were used to obtain the nucleotide sequence and the deduced amino acid sequence. The coding sequence was compared to the gene sequence to define the number and size of introns and exons.The gene spanned 45.5 kb of DNA and consisted of 46 exons. The cDNA encoded a protein of 2721 amino acids.The protein was identified as a lipocalin with novel features. Most lipocalins are proteins with high affinity to small lipophilic molecules, with a molecular size in the 25 kDa range and a well conserved tertiary structure. The apoprotein described here revealed 15 lipocalin like structures, in line. We called this protein a polycalin (pentadecacalin).     

Characterization of the gene for human plasminogen, a key proenzyme in the fibrinolytic system

The organization and structure of the gene coding for plasminogen has been determined by a combination of in vitro amplification of leukocyte DNA from normal individuals and isolation of unique clones from three different human genomic libraries. These clones were characterized by restriction mapping, Southern blotting, and DNA sequencing. The gene for human plasminogen spanned about 52.5 kilobases of DNA and consisted of 19 exons separated by 18 introns. DNA sequence analysis revealed that the five kringle structures in plasminogen were coded by two exons. The nucleotides in the introns at the intron-exon boundaries were GT-AG analogous to those found in other eukaryotic genes. Three polyadenylation sites for plasminogen mRNA were also identified. When the amino acid sequences deduced from the genomic DNA and cDNAs of plasminogen were compared with that of the plasma protein determined by amino acid sequence analysis, an apparent amino acid polymorphism was observed in several positions of the polypeptide chain. Nucleotide sequence analysis of the amplified genomic DNAs and genomic clones also revealed that the plasminogen gene was very closely related to several other proteins, including apolipoprotein(a). This protein may have evolved via duplication and exon shuffling of the plasminogen gene. The presence of another plasminogen-related gene(s) in the human genomic library was also observed.     

Complete nucleotide sequence of a functional HLA-DP beta gene and the region between the DP beta 1 and DP alpha 1 genes: comparison of the 5'' ends of HLA class II genes.

The complete nucleotide sequence of an HLA-DP beta 1 gene and part of the adjacent DP alpha 1 gene, up to and including the signal sequence exon, were determined. The sequence of the DP beta 1 gene identified it as the DPw4 allele. The six exons of the DP beta 1 gene spanned over 11,000 bp of sequence. The arrangement of the gene was broadly analogous to genes of other class II beta chains. The beta 1 exon was flanked by introns of over 4 kb. Comparisons with published sequences of cDNA clones indicated that an alternative splice junction, at the 3' end of the gene, is used in at least one allele. Variation in choice of splice junction indicates an additional mechanism for allelic variation in class II genes. The sequence also indicated that the DP beta 1 and DP alpha 1 genes are separated by only 2 kb at their 5' ends. Comparison of the 5' ends of the DP alpha 1 and beta 1 genes with other class II sequences, including the DZ alpha gene, showed conservation of several blocks of sequences thought to be involved in control of expression. Some areas of the introns were partially conserved in the DQ beta gene, and several other intron sequences were homologous to sequences found in other unrelated genes.     

Gene structure of two-domain arginine kinases from Anthopleura japonicus and Pseudocardium sachalinensis

Unusual two-domain arginine kinases (AKs) arose independently at least two times during molecular evolution of phosphagen kinases: AKs from the primitive sea anemone Anthopleura japonicus and from the clam Pseudocardium sachalinensis. To elucidate its unusual evolution, the structures of Anthopleura and Pseudocardium AK genes have been determined. The Anthopleura gene consisted of 4 exons and 3 introns: two domains are linked by a bridge intron, and each domain contains one intron in different positions. On the other hand, the Pseudocardium gene consisted of 10 exons and 9 introns: two domains are also linked by a bridge intron, and domains 1 and 2 contains 3 and 5 introns, respectively, of which 3 introns are located in exactly same positions. Since the two domains of Pseudocardium AK are estimated to have diverged about 290 million years ago, the 3 introns have been conserved at least for this long. Comparison of intron positions in Anthopleura, Pseudocardium and C. elegans AK genes indicates that there is no intron conserved through the three AK lineages, in sharp contrast to relatively conservative intron positions in creatine kinase (CK) gene family.     

The Human Actin-Regulatory Protein Cap G: Gene Structure and Chromosome Location

Cap G (formerly called macrophage capping protein or gCap39) is a member of the gelsolin/villin fanlily of actin-regulatory proteins. Unlike all other members of this family, Cap G caps the barbed ends of actin filaments, but does not sever them. This protein is half the molecular weight and contains half the number of repeat subunits (3 vs 6) of gelsolin and villin, suggesting that these two proteins may have arisen by gene duplication of the Cap G gene. To investigate this possibility we have cloned and sequenced the human Cap G gene (gene symbol CAPG). The gene is 16.6 kb in size, contains 10 exons and 9 introns and is located on the proximal short arm of chromosome 2. The open reading frame is 6.9 kb, having 9 exons and 8 introns. This region contains 3 splice sites that are nearly identical to the human gelsolin gene, but shares only one with villin, indicating that CAPG is more closely related to gelsolin. Further comparisons of these three genes, however, indicate that the evolutionary steps resulting in human gelsolin and villin are likely to have been more complex than a simple tandem duplication of the Cap G gene.