The globin gene family of the cephalochordate amphioxus: implications for chordate globin evolution

Background  

The lancelet amphioxus (Cephalochordata) is a close relative of vertebrates and thus may enhance our understanding of vertebrate gene and genome evolution. In this context, the globins are one of the best studied models for gene family evolution. Previous biochemical studies have demonstrated the presence of an intracellular globin in notochord tissue and myotome of amphioxus, but the corresponding gene has not yet been identified. Genomic resources of Branchiostoma floridae now facilitate the identification, experimental confirmation and molecular evolutionary analysis of its globin gene repertoire.     

Rise and fall of the delta globin gene

The complete nucleotide sequence of the gene phoE, which codes for the phosphate limitation inducible outer membrane pore protein of Escherichia coli K12 was established. The results show that PhoE protein is synthesized in a precursor form with a 21 amino acid residue amino-terminal extension. This peptide has the general characteristics of a signal sequence. The promoter region of phoE has no homlogy with the consensus sequence of E. coli promoter regions, but homologous sequences with the promoter region of phoA, the structural gene for alkaline phosphatase, were observed. The deduced amino acid sequence showed that the mature PhoE protein is composed of 330 amino acid residues with a calculated molecular weight of 36,782. A number of 81 charged amino acids was found scattered throughout the protein while no large stretches of hydrophobic amino acids were observed. Hydrophobicity and hydration profiles of PhoE protein showed five pronounced hydrophilic maxima which are all located in the region from the amino terminus to residue 212.When the deduced amino acid sequence of PhoE protein was compared with the established sequence of the OmpF pore protein, a number of 210 identical residues was found. Some aspects of the structure-function relationship of PhoE protein are discussed in view of the hydrophobicity and hydration profiles, and the homology between PhoE protein and OmpF protein.     

High-performance liquid chromatography of globin chains in the identification of human globin gene abnormalities

This article summarizes experience and data obtained using a previously developed reverse-phase high-performance liquid chromatography method (J.B. Shelton, J.R. Shelton and W.A. Schroeder, J. Liq. Chromatogr. 7 (1984) 1969) in the study of a number of hemoglobinopathies in the Sardinian population. The occurrence and incidence of several abnormal hemoglobins are described, as well as aspects of the expression of abnormal gamma-globin gene arrangements and thalassemic genes.     

Structure and evolution of the horse zeta globin locus

The equine zeta globin gene locus consists of an intact 5' gene and a truncated 3' pseudogene (psi zeta) that has only 5' control sequences and a first exon and intron. Nevertheless, the psi zeta gene has retained almost perfect homology with its neighbour, presumably by gene conversion. The first introns of both zeta and psi zeta genes contain a number of degenerate tandem repeats of a 14 base-pair sequence that has been found in the zeta genes of goats and humans and that is related to a family of human minisatellite sequences. Comparisons of sequences flanking the zeta and psi zeta genes reveal areas of considerable interspecies homology, which can be explained by a zeta gene duplication that pre-dated the mammalian radiation.     

染色质结构与珠蛋白基因表达调控

综述了β－珠蛋白基因表达调控中,与染色质结构调控相关的区域,染色质重组复合体,染色质修饰等因素及它们之间协同作用的研究。     

A membrane-bound vertebrate globin

The family of vertebrate globins includes hemoglobin, myoglobin, and other O(2)-binding proteins of yet unclear functions. Among these, globin X is restricted to fish and amphibians. Zebrafish (Danio rerio) globin X is expressed at low levels in neurons of the central nervous system and appears to be associated with the sensory system. The protein harbors a unique N-terminal extension with putative N-myristoylation and S-palmitoylation sites, suggesting membrane-association. Intracellular localization and transport of globin X was studied in 3T3 cells employing green fluorescence protein fusion constructs. Both myristoylation and palmitoylation sites are required for correct targeting and membrane localization of globin X. To the best of our knowledge, this is the first time that a vertebrate globin has been identified as component of the cell membrane. Globin X has a hexacoordinate binding scheme and displays cooperative O(2) binding with a variable affinity (P(50)～1.3-12.5 torr), depending on buffer conditions. A respiratory function of globin X is unlikely, but analogous to some prokaryotic membrane-globins it may either protect the lipids in cell membrane from oxidation or may act as a redox-sensing or signaling protein.     

Increase in globin chains and globin mRNA in erythroleukemia cells in response to hemin.

Addition of 50 μm hemin to mouse erythroleukemia cells cultured in 0.5% dimethyl-sulfoxide (DMSO) resulted in >10-fold stimulation of globin chain synthesis as a percentage of acid precipitable protein. In cultures fully induced with 1.5% DMSO, addition of 15 mm 3-amino-1,2,4-triazole (AT), an inhibitor of heme synthesis, reduced globin chain synthesis to uninduced levels and reduced globin mRNA levels to less than 20% of induced values. The inhibition of AT was prevented by simultaneous addition of 25 μm hemin to the cultures. Using RNA-DNA hybridization analysis, the amount of globin mRNA sequences as a fraction of total cytoplasmic RNA was also increased by addition of 50 μm hemin to cultures with 0.5% DMSO. The results suggest that exogenous hemin can promote globin chain synthesis, that endogenously synthesized heme can be required for globin chain synthesis, and that hemin directly or indirectly also alters the appearance or degradation of globin mRNA sequences in the cytoplasm.     

Nucleotide sequence of the goat embryonic alpha globin gene (zeta) and linkage and evolutionary analysis of the complete alpha globin cluster

In previous studies we identified and sequenced clones containing two adult alpha globin genes of the goat. Additional studies have revealed the presence of an embryonic alpha globin gene termed zeta. Sequence analysis of the gene shows that it is the largest mammalian or avian globin gene cloned to date. Its unusual size is mainly due to a 14 base-pair tandem repeat sequence in its first intron. A similar sequence is also found in the first intron of the human zeta gene. The goat zeta coding sequence differs greatly from that of the adult alpha, particularly at amino acid position 38, where it codes for the amino acid replacement of Gln for Thr. This change may confer a higher intrinsic O2 affinity on the zeta globin protein, ensuring a sufficient O2 supply for the developing goat embryo. The cloning and sequencing of this gene completes the alpha globin locus of the goat, composed of three genes in the following order 5'-zeta-I alpha-II alpha-3'. Evolutionary comparisons of the goat alpha locus with other amphibian, avian and mammalian loci reveal several interesting features. Statistical analysis confirms the hypothesis that the embryonic alpha gene is much older (400 million years) than the embryonic beta gene (200 million years), and that it is descended from a primordial gene, whose present-day counterpart is the Xenopus larval alpha globin gene. Our results also suggest that after the divergence of the avian line, the alpha A gene converted the alpha D gene during the evolution of the pre-mammalian line. The alpha D globin gene remains unconverted in the avian line, potentially because of insertion/deletion sequences that may prevent any gene conversion event. The divergence rates of specific globin genes have been analyzed and found to form an essentially straight line, in agreement with the neutralist view of evolution.