ABSTRACT
We have identified a remote, tissue-specific, positive regulatory element that is of major importance in determining the level of human alpha-globin gene expression. Stable transformants containing this DNA segment linked to the alpha gene in mouse erythroleukemia cells expressed human alpha mRNA at levels that are indistinguishable from those seen in interspecific hybrids containing the human alpha genes in their normal context on chromosome 16. Furthermore, all transgenic mice containing the alpha genes linked to this region expressed alpha-globin mRNA at high levels in erythroid tissues; and in one such mouse, readily detectable levels of human alpha-globin chains could be demonstrated in the peripheral blood. There is considerable similarity in the position, structure, and function of this region upstream of the alpha-globin complex with previously described elements within the beta-globin dominant control region (DCR). This is m marked contrast to other structural and functional differences between the two gene clusters. It seems likely that these critical, positive regulatory regions might provide target sequences through which coordinate regulation of the alpha- and beta-like globin genes is achieved.
Subject(s)
Globins/genetics , Animals , Deoxyribonuclease I , Erythrocytes/metabolism , Gene Expression Regulation/genetics , Humans , Leukemia, Erythroblastic, Acute , Mice , Mice, Transgenic , Multigene Family , Organ Specificity , Regulatory Sequences, Nucleic Acid , Transfection , Tumor Cells, CulturedABSTRACT
We describe a family in which alpha-thalassemia occurs in association with a deletion of 62 kilobases from a region upstream of the alpha globin genes. DNA sequence analysis has shown that the transcription units of both alpha genes downstream of this deletion are normal. Nevertheless, they fail to direct alpha globin synthesis in an interspecific hybrid containing the abnormal (alpha alpha)RA chromosome. It seems probable that previously unidentified positive regulatory sequences analogous to those detected in a corresponding position of the human beta globin cluster are removed by this deletion.
Subject(s)
Chromosome Deletion , Globins/genetics , Thalassemia/etiology , Animals , Base Sequence , Chromosome Mapping , Chromosomes, Human, Pair 16 , Down-Regulation/genetics , Genotype , Humans , Hybrid Cells/physiology , Mice , Molecular Sequence Data , Mutation , Phenotype , Thalassemia/geneticsABSTRACT
The DNA sequence was determined for the cloned Thiobacillus ferrooxidans nifH and part of the nifD genes. A putative T. ferrooxidans nifH promoter was identified whose sequences showed perfect consensus with those of the Klebsiella pneumoniae nif promoter. Two putative consensus upstream activator sequences were also identified. The amino acid sequence was deduced from the DNA sequence. In a comparison of nifH DNA sequences from T. ferrooxidans and eight other nitrogen-fixing microbes, a Rhizobium sp. isolated from Parasponia andersonii showed the greatest homology (74%) and Clostridium pasteurianum (nifH 1) showed the least homology (54%). In a comparison of the amino acid sequences of the Fe proteins, the Rhizobium sp. and Rhizobium japonicum showed the greatest homology (both 86%) and C. pasteurianum (nifH 1 gene product) demonstrated the least homology (56%) to the T. ferrooxidans Fe protein.
Subject(s)
Nitrogenase/genetics , Thiobacillus/genetics , Amino Acid Sequence , Base Sequence , Cloning, Molecular , DNA, Bacterial/analysis , Klebsiella pneumoniae/genetics , Rhizobium/analysis , Thiobacillus/enzymologyABSTRACT
The presence of nucleotide sequences which are homologous to the nifHDK genes of Klebsiella pneumoniae was demonstrated in total DNA preparations from five different iron-oxidizing Thiobacillus ferrooxidans strains. A non-iron-oxidizing Thiobacillus novellus strain and a heterotrophic Acidiphilium strain, which occurs in close association with T. ferrooxidans, did not contain DNA homologous to the nifHDK genes. The T. ferrooxidans ATCC33020 nifHDK genes were cloned and their arrangement was characterized on a 6.7-kb insert in pIMP16.
