Β-type Genes Research Articles

Mechanisms mediating suppression of globin gene transcription in Danio rerio nonerythroid cells

We studied the repression of adult and embryo-larval genes of the major globin gene locus in D. rerio fibroblasts. The results obtained suggest that at least some of the globin genes are repressed by Polycomb, similarly to human α-globin genes. Furthermore, within two α/β globin gene pairs, repression of α-type and β-type genes appears to be mediated by different mechanisms, as increasing the level of histone acetylation can activate transcription of only β-type genes.

Chromosomal arrangement of the chicken β-type globin genes

We have isolated the chicken β-type globin genes from a library of chicken DNA-λ Charon 4A recombinant bacteriophage. There are four β-type genes within this segment of the genome; we believe this represents all of the β-type genes of the chicken. The recombinant λCβG1 contains the embryonic ϵ- and adult β-globin genes. The hatching β H and embryonic p-globin genes are found in the recombinant λCβG2. Although λCβG1 and λCβG2 do not physically overlap, we present evidence that all four genes are closely linked and transcribed from the same DNA strand. These experiments demonstrate that the chromosomal regions represented by λCβG1 and λCβG2 lie approximately 1.6 kb apart in the chicken genome. A third recombinant λCβG3 extends the genomic locus studied in the vicinity of the β-type globin genes to approximately 39 kb. The physical order of the chicken β-type globin genes within this segment of the chromosome is 5′ … ϱ- β H- β- ϵ … 3′. This arrangement is unique among the vertebrate β-type globin gene clusters thus far examined, in that embryonic genes are located at the 5′ and 3′ ends of the cluster while the hatching and adult genes occupy central positions.

Biliproteins of cyanobacteria and Rhodophyta: Homologous family of photosynthetic accessory pigments

Amino-terminal sequence determinations are reported of the subunits of biliproteins of prokaryotic unicellular and filamentous cyanobacteria and of eukaryotic unicellular red algae. The biliproteins examined, allophycocyanin, C-phycocyanin, R-phycocyanin, b-phycoerythrin, and phycoerythrocyanin, vary with respect to the chemical nature and the number and distribution of the bilin chromophores between the two dissimilar subunits. The amino-terminal sequences fall into two classes, "alpha-type" and "beta-type", with a high degree of homology within each class.In those biliproteins where the number of bilin chromophores on the two subunits is unequal, the subunit with the greater number of chromophores has the beta-type amino-acid sequence.Extensive homology also exists between alpha- and beta-type sequences, strongly supporting the view that these arose by gene duplication to give rise to the ancestral alpha- and beta-type genes early in the evolution of the biliproteins. The subsequent generation of the various classes of biliproteins appears to be the result of further gene duplication of the alpha- and beta-type genes, ultimately to give rise to families of polypeptide chains of similar sequence, but varying in the number of chromophore attachment sites and the structure of the chromophores.