Isolation and characterization of the gene encoding bovine adenylate kinase isozyme 2

cDNA cloning and tissue-specific expression of the gene encoding human adenylate kinase isozyme 2

We isolated two kinds of cDNAs encoding human adenylate kinase (AK) isozyme 2 from a HeLa cell cDNA library using bovine AK2 cDNA as a probe. Nucleotide sequencing revealed that the cDNAs encoded 239- and 232-amino acid proteins with deduced molecular mass of 26.5 (AK2A) and 25.6kDa (AK2B), respectively. Northern blot analysis demonstrated that AK2 mRNA is strongly expressed in liver, heart, skeletal muscle and pancreas, and moderately in kidney, placenta and brain, and weakly in lung. However, Western blot analysis showed that AK2 protein was present in large amounts in liver, heart, kidney, and in a small amount in lung, and undetectable in brain and skeletal muscle. These results suggested the presence of the tissue-specific gene-expression including post-transcriptional regulation in expression of the AK2 gene.

Phosphate depletion enhances the stability of the amphotropic murine leukemia virus receptor mRNA

Through its specific receptor, the amphotropic murine leukemia virus (MLV) infects cells from many mammals, including humans. We have previously demonstrated that levels of human amphotropic MLV receptor (pit2) mRNA varied considerably in different human cell lines. Removal of phosphate from the culture medium led to increases in the amount of pit2 mRNA and the quantity of a 71-kDa protein specifically recognized by antibodies against Pit2. To determine if the increases in pit2 mRNA and protein levels were due to a transcriptional effect, the pit2 promoter region was cloned. This region was characterized and found to contain a functional TATA-less promoter that under our experimental conditions does not respond to phosphate depletion. Instead, pit2 mRNA was found to be more stable in response to Pi depletion. These results suggest that the increase in pit2 mRNA levels observed in response to Pi depletion occurs at a posttranscriptional level and is due to enhanced mRNA stability.

The structure of bovine mitochondrial adenylate kinase: comparison with isoenzymes in other compartments

In vertebrates, there are different adenylate kinases in the compartments cytosol, mitochondrial intermembrane space, and mitochondrial matrix. Here, we report the spatial structure of the intermembrane species established in two crystal forms by X-ray diffraction analyses at 1.92 and 2.1 A resolution. In both structures, the enzyme is unligated, and thus in an "open" conformation. The enzyme was prepared from bovine liver, containing at least five variants arisen from posttranscriptional and posttranslational modifications. It could only be crystallized after removing some of these variants. A comparison with the known structures of the adenylate kinases from cytosol and mitochondrial matrix reveals structural differences that should play a role in protein targeting because none of these enzymes contains a cleavable signal peptide. A further comparison with adenylate kinases from Gram-positive bacteria showed that the structural Zn2+ ion of these species is replaced by a strictly conserved assembly of hydrogen bonded residues.

A conserved downstream element defines a new class of RNA polymerase II promoters

Although many TATA-less promoters transcribed by RNA polymerase II initiate transcription at multiple sites, the regulation of multiple start site utilization is not understood. Beginning with the prediction that multiple start site promoters may share regulatory features and using the P-glycoprotein promoter (which can utilize either a single or multiple transcription start site(s)) as a model, several promoters with analogous transcription windows were grouped and searched for the presence of a common DNA element. A downstream protein-binding sequence, MED-1 (Multiple start site Element Downstream), was found in the majority of promoters analyzed. Mutation of this element within the P-glycoprotein promoter reduced transcription by selectively decreasing utilization of downstream start sites. We propose that a new class of RNA polymerase II promoters, those that can utilize a distinctive window of multiple start sites, is defined by the presence of a downstream MED-1 element.

Iron deprivation results in an increase in p53 expression

Deferoxamine (DFO)-induced iron deprivation caused an increase in p53 expression in ML-1 and Raji cells. In ML-1 cells, with express wild type p53, p53 protein levels were transiently increased 6 h after addition of 10(-4)M DFO. In Raji cells, which carry a mutant p53 allele, p53 increased 6 h after addition of 10(-4)M DFO and remained elevated for 24 h. Growth inhibition was observed in both cell types 6 h after addition of 10(-4)M DFO. In both cells, p53 mRNA levels did not increase following incubation with DFO, suggesting that increased p53 expression is the result of a post-transcriptional mechanism. Although increases in wild type p53 protein in ML-1 cells resulted in increases in a p53 target gene, p21cipl/wafl/sdil, this effect was not observed in Raji cells which express a mutant p53 protein.

Cloning and characterization of the gene encoding bovine mitochondrial adenylate kinase isozyme 3

The structure of the gene (AK3) encoding bovine mitochondrial (mt) adenylate kinase isozyme 3 (AK3) has been determined. The gene spans about 46 kb and splits into five exons. The 5'-flanking region of the gene lacks typical transcriptional regulatory elements such as TATA and CAAT boxes. The G + C content of this region is high (71%), and seven GC boxes are recognized. Possible sequences responsive to transcription factors, AP-1, AP-2, Myf-6 and MyoD1, are present in this region. In the 5'-flanking region, there are sequences (mt sequence) which were found in the genes encoding other mt proteins. Transcriptional mapping analyses revealed one major mRNA start point. The promoter activity measurement in Chinese hamster ovary cells by transient expression of the cat gene connected with the 5'-flanking region, showed presence of a functional promoter.

Characterization of a processed pseudogene derived from the gene encoding bovine adenylate kinase isozyme 2

We have isolated an intronless processed pseudogene for an isoform of bovine adenylate kinase isozyme 2 (AK2B). The pseudogene which was flanked by 11-nucleotide (nt) direct repeats contained an open reading frame of 519 bp which encodes 173 amino acids (aa), 61 aa shorter than AK2B. In the entire pseudogene sequence, substitutions as well as deletions and insertions were noted in 78 nt positions as compared with the AK2B cDNA (95.1% homology). Northern-blot analysis showed that this pseudogene was not expressed in bovine tissues.