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Higher order structure of chromosomes.

Isolated Chinese hamster metaphase chromosomes were resuspended in 4 M ammonium acetate and spread on a surface of distilled water or 0.15 to 0.5 M ammonium acetate. The DNA was released in the form of a regular series of rosettes connected by interrossette DNA. The mean length of the rosette DNA was 14 micron, similar to the mean length of 10 micron for chromomere DNA of Drosophila polytene chromosomes. The mean interrosette DNA was 4.2 micron. SDS gel electrophoresis of the chromosomal nonhistone proteins showed them to be very similar to nuclear nonhistone proteins except for the presence of more actin and tubulin. Nuclear matrix proteins were present in the chromosomes and may play a role in forming the rosettes. Evidence that the rosette pattern is artifactual versus the possibility that it represents a real organizational substructure of the chromosomes is reviewed.

Actins↗

Structure and chromosomal location of the bovine gene for the heart muscle isoform of cytochrome c oxidase subunit VIII.

We have isolated the bovine COX8H gene for the heart/muscle isoform of cytochrome c oxidase (COX) subunit VIII from a library of bovine genomic DNA cloned into lambda EMBL3. Primer extension assays on bovine heart mRNA mapped the 5' ends of COX8H transcripts to a CA dinucleotide 62-bp upstream from the ATG codon. The gene thus spans 1565-bp and comprises two exons and one large intron of 1227 bp. Exon 1 encodes the 5' untranslated region, a 24-amino acid presequence, and the first 13 amino acids of the mature COX VIII-H protein. Exon 2 encodes the remainder of the cDNA: amino acids 14 to 46 plus the 66-bp 3' untranslated region. The exon-intron boundaries matched the consensus splice junction sequences. Two protein polymorphisms were seen: an Ala/Val polymorphism at position -6 in the presequence and the previously noted Lys/Arg polymorphism at residue 7 of the mature protein. A TaqI polymorphism occurs in the intron. The COX8H gene was mapped by bovine x rodent somatic cell hybrid mapping panels to bovine (BTA) Chromosome (Chr) 25 with 100% concordancy. BTA 25 is conserved relative to the long arm of human (HSA) Chr 11, which contains COX8, the gene for the single human COX VIII subunit that is homologous to the liver isoform.

Amino Acid Sequence↗

Genomic structure and chromosomal localization of processed pseudogenes for human RBP-Jk.

The functional gene for human recombination signal sequence-binding protein (RBP-Jk) and corresponding processed psudogenes have been isolated from various species, such as Drosophila, Xenopus, mouse, and human. Here we report the isolation of another two genomic pseudogenes of human RBP-Jk, named K2 and K7, from a cosmid library of Hela cells. The nucleotide sequences of both genes exhibited more than 95% homology to the functional human gene for RBP-Jk. Moreover, they did not contain any intron sequences and were interrupted by several stop codons in all frames. In situ hybridization demonstrated that the pseudogenes, K2 and K7, were localized at chromosomes 9p13 and 9q13, respectively. Their physical maps differed from those of the true functional gene and of the pseudogenes reported previously by Amakawa et al. (1993).

Base Sequence↗

Characterization of the mouse beta-prime adaptin gene; cDNA sequence, genomic structure, and chromosomal localization.

Adaptins are important subunits of heterotetrameric complexes called adaptors, which participate in the clathrin-coated, vesicle-mediated endocytosis and intracellular receptor transport. The gene family of adaptins is divided into three classes, alpha, beta, and gamma, with further subdivision into beta- and beta-prime components. Two beta-prime adaptins, the rat AP105a and the human BAM22, have previously been characterized. The BAM22 gene is located on human Chromosome (Chr) 22q12 and can be considered a candidate meningioma tumor suppressor gene. We report here the characterization of the mouse ortholog of the BAM22 gene, and we suggest the name adtb1 for the mouse gene. Like the BAM22 gene, the adtb1 transcript is highly and ubiquitously expressed. We provide 3885-bp cDNA sequence, which entirely covers the open reading frame of the adtb1, capable of encoding a protein of 943 amino acids. The adtb1 protein is highly conserved (>96% identity) when compared with AP105a and BAM22 proteins. We also report the genomic organization of adtb1, which is similar to the BAM22 gene. The adtb1 gene has been assigned to mouse Chr 11, band 11A2, which confirms the synteny between human Chr 22q12 and mouse Chr 11.

Adaptor Protein Complex 1↗

Genomic structure and chromosomal localization of the mouse Ogg1 gene that is involved in the repair of 8-hydroxyguanine in DNA damage.

8-Hydroxyguanine (7,8-dihydro-8-oxoguanine: oh8Gua) is a damaged form of guanine induced by oxygen-free radicals and causes GC to TA transversions. Previously we isolated the hOGG1 gene, a human homolog of the yeast OGG1 gene, which encodes a DNA glycosylase and lyase to excise oh8Gua in DNA. In this study, we isolated a mouse homolog (Ogg1) of the OGG1 gene, characterized oh8Gua-specific DNA glycosylase/AP lyase activities of its product, and determined chromosomal localization and exon-intron organization of this gene. A predicted protein possessed five domains homologous to human and yeast OGG1 proteins. Helix-hairpin-helix and C2H2 zinc finger-like DNA-binding motifs found in human and yeast OGG1 proteins were also retained in mouse Ogg1 protein. The properties of a GST fusion protein were identical to human and yeast OGG1 proteins in glycosylase/lyase activities, their substrate specificities, and suppressive activities against the spontaneous mutagenesis of an Escherichia coli mutM mutY double mutant. The mouse Ogg1 gene was mapped to Chromosome (Chr) 6, and consisted of 7 exons approximately 6 kb long. Two DNA-binding motifs were encoded in exons 4 through 5. These data will facilitate the investigation of the OGG1 gene to elucidate the relationship between oxidative DNA damage and carcinogenesis.

Amino Acid Sequence↗